Travis: run the script as a single command
Travis: run the script as a single command

This way doctr isn't run if the docs build fails.

See https://github.com/travis-ci/travis-ci/issues/1066.

madan96/sympy,jaimahajan1997/sympy,kaushik94/sympy,skidzo/sympy,yashsharan/sympy,kaushik94/sympy,kaushik94/sympy,chaffra/sympy,jaimahajan1997/sympy,chaffra/sympy,yashsharan/sympy,madan96/sympy,skidzo/sympy,chaffra/sympy,yashsharan/sympy,madan96/sympy,jaimahajan1997/sympy,skidzo/sympy