Travis: Force to use clang/clang++ when compiler is clang
Travis: Force to use clang/clang++ when compiler is clang

shogun-toolbox/shogun,Saurabh7/shogun,Saurabh7/shogun,besser82/shogun,Saurabh7/shogun,besser82/shogun,karlnapf/shogun,lisitsyn/shogun,geektoni/shogun,karlnapf/shogun,lisitsyn/shogun,geektoni/shogun,sorig/shogun,Saurabh7/shogun,shogun-toolbox/shogun,besser82/shogun,geektoni/shogun,shogun-toolbox/shogun,besser82/shogun,shogun-toolbox/shogun,lisitsyn/shogun,sorig/shogun,lisitsyn/shogun,karlnapf/shogun,karlnapf/shogun,sorig/shogun,lambday/shogun,Saurabh7/shogun,karlnapf/shogun,shogun-toolbox/shogun,lisitsyn/shogun,sorig/shogun,lambday/shogun,lambday/shogun,lambday/shogun,sorig/shogun,Saurabh7/shogun,lisitsyn/shogun,Saurabh7/shogun,lambday/shogun,sorig/shogun,geektoni/shogun,Saurabh7/shogun,geektoni/shogun,besser82/shogun,besser82/shogun,karlnapf/shogun,lambday/shogun,shogun-toolbox/shogun,Saurabh7/shogun,geektoni/shogun