Allow dashes in environment variable names
Allow dashes in environment variable names

See http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html
Environment variable names used by the utilities in the Shell and
Utilities volume of POSIX.1-2008 consist solely of uppercase letters,
digits, and the <underscore> ( '_' ) from the characters defined in
Portable Character Set and do not begin with a digit. Other characters may
be permitted by an implementation; applications shall tolerate the
presence of such names.

Signed-off-by: Joffrey F <2e95f49799afcec0080c0aeb8813776d949e0768@docker.com>

sdurrheimer/compose,thaJeztah/compose,shubheksha/docker.github.io,funkyfuture/docker-compose,shin-/docker.github.io,TomasTomecek/compose,JimGalasyn/docker.github.io,phiroict/docker,JimGalasyn/docker.github.io,docker-zh/docker.github.io,docker-zh/docker.github.io,GM-Alex/compose,kojiromike/compose,thaJeztah/docker.github.io,swoopla/compose,bdwill/docker.github.io,michael-k/docker-compose,docker/docker.github.io,thaJeztah/compose,denverdino/docker.github.io,aduermael/docker.github.io,denverdino/denverdino.github.io,anweiss/docker.github.io,denverdino/compose,joeuo/docker.github.io,vdemeester/compose,alexisbellido/docker.github.io,twitherspoon/compose,londoncalling/docker.github.io,menglingwei/denverdino.github.io,rillig/docker.github.io,joeuo/docker.github.io,joaofnfernandes/docker.github.io,gdevillele/docker.github.io,jzwlqx/denverdino.github.io,menglingwei/denverdino.github.io,denverdino/denverdino.github.io,joeuo/docker.github.io,ChrisChinchilla/compose,bdwill/docker.github.io,LuisBosquez/docker.github.io,shin-/docker.github.io,sanscontext/docker.github.io,rillig/docker.github.io,docker/docker.github.io,TomasTomecek/compose,shin-/docker.github.io,menglingwei/denverdino.github.io,sanscontext/docker.github.io,mdaue/compose,rillig/docker.github.io,ChrisChinchilla/compose,docker/docker.github.io,hoogenm/compose,joaofnfernandes/docker.github.io,docker-zh/docker.github.io,anweiss/docker.github.io,shin-/docker.github.io,shubheksha/docker.github.io,andrewgee/compose,shin-/compose,schmunk42/compose,sanscontext/docker.github.io,londoncalling/docker.github.io,mdaue/compose,thaJeztah/docker.github.io,troy0820/docker.github.io,schmunk42/compose,BSWANG/denverdino.github.io,denverdino/compose,vdemeester/compose,bdwill/docker.github.io,denverdino/docker.github.io,GM-Alex/compose,alexisbellido/docker.github.io,moxiegirl/compose,moxiegirl/compose,LuisBosquez/docker.github.io,londoncalling/docker.github.io,LuisBosquez/docker.github.io,sanscontext/docker.github.io,johnstep/docker.github.io,denverdino/denverdino.github.io,alexandrev/compose,anweiss/docker.github.io,denverdino/denverdino.github.io,troy0820/docker.github.io,menglingwei/denverdino.github.io,phiroict/docker,phiroict/docker,tiry/compose,joaofnfernandes/docker.github.io,denverdino/docker.github.io,aduermael/docker.github.io,jzwlqx/denverdino.github.io,LuisBosquez/docker.github.io,thaJeztah/docker.github.io,alexisbellido/docker.github.io,swoopla/compose,denverdino/denverdino.github.io,danix800/docker.github.io,docker-zh/docker.github.io,sanscontext/docker.github.io,gdevillele/docker.github.io,denverdino/docker.github.io,funkyfuture/docker-compose,londoncalling/docker.github.io,phiroict/docker,BSWANG/denverdino.github.io,joeuo/docker.github.io,jonaseck2/compose,dbdd4us/compose,anweiss/docker.github.io,KalleDK/compose,michael-k/docker-compose,troy0820/docker.github.io,JimGalasyn/docker.github.io,docker/docker.github.io,mrfuxi/compose,dnephin/compose,danix800/docker.github.io,joeuo/docker.github.io,menglingwei/denverdino.github.io,joaofnfernandes/docker.github.io,alexisbellido/docker.github.io,londoncalling/docker.github.io,dbdd4us/compose,joaofnfernandes/docker.github.io,troy0820/docker.github.io,hoogenm/compose,rillig/docker.github.io,thaJeztah/docker.github.io,phiroict/docker,shubheksha/docker.github.io,anweiss/docker.github.io,thaJeztah/docker.github.io,shubheksha/docker.github.io,gdevillele/docker.github.io,johnstep/docker.github.io,johnstep/docker.github.io,johnstep/docker.github.io,jrabbit/compose,shin-/docker.github.io,jzwlqx/denverdino.github.io,danix800/docker.github.io,alexandrev/compose,twitherspoon/compose,tiry/compose,bdwill/docker.github.io,jzwlqx/denverdino.github.io,LuisBosquez/docker.github.io,jonaseck2/compose,shin-/compose,jeanpralo/compose,aduermael/docker.github.io,andrewgee/compose,JimGalasyn/docker.github.io,JimGalasyn/docker.github.io,sdurrheimer/compose,jrabbit/compose,BSWANG/denverdino.github.io,gdevillele/docker.github.io,johnstep/docker.github.io,aduermael/docker.github.io,danix800/docker.github.io,jzwlqx/denverdino.github.io,docker-zh/docker.github.io,BSWANG/denverdino.github.io,KalleDK/compose,docker/docker.github.io,denverdino/docker.github.io,jeanpralo/compose,BSWANG/denverdino.github.io,alexisbellido/docker.github.io,mrfuxi/compose,kojiromike/compose,gdevillele/docker.github.io,bdwill/docker.github.io,dnephin/compose,shubheksha/docker.github.io