Fix missing noexcept specifier

This commit adds a noexcept specification to
BansheeEngine::Exception::what(), since it overrides
std::exception::what(), which has a noexcept specification since C++11.

Source/BansheeUtility/Include/BsException.h

@@ -88,7 +88,7 @@ namespace BansheeEngine
 		virtual const String& getDescription(void) const { return mDescription; }
 
 		/** Overriden std::exception::what. Returns the same value as getFullDescription(). */
-		const char* what() const override { return getFullDescription().c_str(); }
+		const char* what() const noexcept override { return getFullDescription().c_str(); }
 
 	protected:
 		long mLine;