Use "https" instead of "http" if CTK_USE_GIT_PROTOCOL is OFF

Fixes https://github.com/commontk/CTK/issues/439

CMakeLists.txt

@@ -455,11 +455,11 @@ endif()
 # Other options
 
 # Git protocol option
-option(CTK_USE_GIT_PROTOCOL "If behind a firewall turn this OFF to use http instead." ON)
+option(CTK_USE_GIT_PROTOCOL "If behind a firewall turn this OFF to use https instead." ON)
 mark_as_advanced(CTK_USE_GIT_PROTOCOL)
 set(git_protocol "git")
 if(NOT CTK_USE_GIT_PROTOCOL)
-  set(git_protocol "http")
+  set(git_protocol "https")
 endif()
 
 # Let's mark as advanced some default properties