Fix colourized output to file

This change should be backwards compatible, but it would be better
to make the console colour API take an argument in the long term.

Fixes #1502

include/internal/catch_console_colour.cpp

@@ -160,7 +160,8 @@ namespace {
 
     private:
         void setColour( const char* _escapeCode ) {
-            Catch::cout() << '\033' << _escapeCode;
+            getCurrentContext().getConfig().stream()
+                << '\033' << _escapeCode;
         }
     };