Updated minimum required gcc version to 4.9

The contour fitting uses generic lambdas, which apparently don't work on gcc-4.8.5.

README.md

@@ -26,7 +26,7 @@ At the moment, it mainly provides the following functionality:
 
 ## Usage
 
-* Tested with the following compilers: >=gcc-4.8.4, >=clang-3.5, Visual Studio 2015
+* Tested with the following compilers: >=gcc-4.9, >=clang-3.5, Visual Studio 2015
 * Needed dependencies for the library: Boost system (>=1.50.0), OpenCV core (>=2.4.3)
 
 To use the library in your own project, just add the following directories to your include path: