Add version to clang

Author: martinmoene

README.md

@@ -195,7 +195,7 @@ Reported to work with
 *optional lite* is reported to work with the following compilers: 
 - Visual C++ 6 SP6 (VS6), VC10, (VS2010), VC11 (VS2012), VC12 (VS2013), ...
 - GNUC 4.8.1 with -std=c++98, -std=c++03, -std=c++11, -std=c++1y 
-- clang
+- clang 3.4 with -std=c++03, -std=c++11 (on Travis)
 
 
 Implementation notes