Add Travis CI that ensures compilation success

Despite I don't know how to test that colors are really applied to
terminal, it would be really nice to have at least a simple test
that ensures that we still can compile a test project without
errors.

"-c++=11" compilation flag is removed, since we don't use this
standard and Linux on Travis CI doesn't have appropriate GCC version.

.travis.yml

@@ -0,0 +1,18 @@
+sudo: false
+language: cpp
+
+os:
+  - linux
+  - osx
+
+compiler:
+  - clang
+  - gcc
+
+script:
+  - mkdir build/ && cd build/
+  - cmake ../ -DCMAKE_BUILD_TYPE=Release
+  - make
+
+notifications:
+  email: false

CMakeLists.txt

@@ -10,7 +10,7 @@ if (${CMAKE_CXX_COMPILER_ID} STREQUAL "Clang")
 endif (${CMAKE_CXX_COMPILER_ID} STREQUAL "Clang")
 
 if (CMAKE_COMPILER_IS_GNUCXX OR CMAKE_COMPILER_IS_CLANG)
-  set (CMAKE_CXX_FLAGS "-Wall -Wextra -pedantic -fvisibility=hidden -std=c++11")
+  set (CMAKE_CXX_FLAGS "-Wall -Wextra -pedantic -fvisibility=hidden")
   set (CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_INIT} -g")
   set (CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_INIT} -O2")
 endif (CMAKE_COMPILER_IS_GNUCXX OR CMAKE_COMPILER_IS_CLANG)

include/termcolor/termcolor.hpp

@@ -435,7 +435,7 @@ namespace termcolor
             else if ((&stream == &std::cerr) || (&stream == &std::clog))
                 return stderr;
 
-            return nullptr;
+            return 0;
         }