Bump CMake version to 0.5.0 also. (#360)

This should have been done in #356.

Author: g-easy

CMakeLists.txt

@@ -21,7 +21,7 @@ if(CCACHE_PROGRAM)
   set_property(GLOBAL PROPERTY RULE_LAUNCH_LINK "${CCACHE_PROGRAM}")
 endif()
 
-project(opencensus-cpp VERSION 0.4.0 LANGUAGES CXX)
+project(opencensus-cpp VERSION 0.5.0 LANGUAGES CXX)
 
 option(FUZZER "Either OFF or e.g. -fsanitize=fuzzer,address" OFF)