fix

.travis.yml

@@ -19,7 +19,7 @@ before_install:
 - git submodule foreach git checkout master
 - ln -s ./../expansions .
 
-- wget -O - https://github.com/premake/premake-core/releases/download/v5.0.0-alpha12/premake-5.0.0-alpha12-linux.tar.gz | tar zfx -
+- wget -O - https://github.com/premake/premake-core/releases/download/v5.0.0-alpha13/premake-5.0.0-alpha13-linux.tar.gz | tar zfx -
 - wget -O - https://www.lua.org/ftp/lua-5.3.4.tar.gz | tar zfx -; cd lua-5.3.4; sudo make linux install; cd ..
 - ./premake5 gmake
 - cd build