travis: remove Ruby path tweak

Putting the Ruby 1.8 we use to run tests on 10.9 into the PATH adversely
affects formulae with a Ruby dependency (possibly other formulae, too).
Remove this hack, as it is no longer needed.

Closes Homebrew/homebrew#47694.

Signed-off-by: Martin Afanasjew <martin@afanasjew.de>

.travis.yml

@@ -31,7 +31,6 @@ before_install:
 install:
   - if [ "$HOMEBREW_RUBY" = "1.8.7" ]; then
       brew install homebrew/versions/ruby187;
-      export PATH="/usr/local/opt/ruby187/bin:$PATH";
       export HOMEBREW_RUBY_PATH="/usr/local/opt/ruby187/bin/ruby";
       brew untap homebrew/versions;
     fi