.travis.yml: Try to fix Travis CI builds by using Clang 3.5.
.travis.yml: Try to fix Travis CI builds by using Clang 3.5.

csuideal/log4cplus,csuideal/log4cplus,ccpaging/log4cplus,ccpaging/log4cplus,csuideal/log4cplus,ccpaging/log4cplus,csuideal/log4cplus,ccpaging/log4cplus