Currently lessphp 0.4 doesn't works well with bootstrap 2.3

I force the latest 0.3 version of lessphp to fix this issue.

Here a quote from lessphp 0.4.0 changelog :
Warning: this release has some breaking changes. If you the old selector expression syntax (eg. Bootstrap 2.3) then it’s recommended to use 0.3.9.
Merge pull request #6 from BenoitLeveque/fix-travis-issue-with-lessphp

Currently lessphp 0.4 doesn't works well with bootstrap 2.3