travis: add dirty hack for linux build

Author: eagleivg

.travis.yml

@@ -12,6 +12,7 @@ before_script:
   - sudo apt-get install libegl1-mesa-dev libgles2-mesa-dev libpugixml-dev libopenal-dev libtbb-dev libcrypto++-dev liblockfile-dev libfreeimage-dev
   - sudo apt-get install cmake lua5.1-dev libssl-dev libogg-dev libtheora-dev libvorbis-dev libsdl2-dev liblzo2-dev libjpeg-dev libncurses5-dev
   - mkdir bin
+  - rm -rf Externals/cryptopp/*
   - cd bin
   - cmake ..
 script: