Dockerfile: Symlink ruby2.0 to /usr/bin/ruby
Dockerfile: Symlink ruby2.0 to /usr/bin/ruby

brew tests fails otherwise.

1) Failure:
LanguageModuleRequirementTests#test_good_ruby_deps
[/home/linuxbrew/.linuxbrew/Library/Homebrew/test/test_language_module_requirement.rb:51]:
Expected #<LanguageModuleRequirement: "languagemodule" [:ruby, "date", nil]>
to be satisfied?.

gnubila-france/linuxbrew,Angeldude/linuxbrew,Homebrew/linuxbrew,DoomHammer/linuxbrew,Angeldude/linuxbrew,DoomHammer/linuxbrew,saketkc/linuxbrew,drbenmorgan/linuxbrew,Homebrew/linuxbrew,saketkc/linuxbrew,drbenmorgan/linuxbrew,Linuxbrew/linuxbrew,Linuxbrew/linuxbrew,sjackman/linuxbrew,DoomHammer/linuxbrew,SuperNEMO-DBD/cadfaelbrew,SuperNEMO-DBD/cadfaelbrew,SuperNEMO-DBD/cadfaelbrew,sjackman/linuxbrew,gnubila-france/linuxbrew,reelsense/linuxbrew,reelsense/linuxbrew,reelsense/linuxbrew,saketkc/linuxbrew,saketkc/linuxbrew,drbenmorgan/linuxbrew,Angeldude/linuxbrew,reelsense/linuxbrew,Linuxbrew/linuxbrew,Linuxbrew/linuxbrew,SuperNEMO-DBD/cadfaelbrew,Homebrew/linuxbrew,Angeldude/linuxbrew,sjackman/linuxbrew,gnubila-france/linuxbrew,sjackman/linuxbrew,gnubila-france/linuxbrew,Homebrew/linuxbrew,DoomHammer/linuxbrew,drbenmorgan/linuxbrew