Bump version to 0.6.3 as per https://github.com/docopt/docopt.cpp/issues/163
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.1)
-project(docopt.cpp VERSION 0.6.2)
+project(docopt.cpp VERSION 0.6.3)
 
 include(GNUInstallDirs)