Keep snippet vars definitions in a single format across all snippets and documentation.

The format is:

# var-name: value

Previously snippets used a mixture of the following formatting:

#var-name: value
#var-name : value
# var-name: value
# var-name : value

snippets/snippet-mode/field

@@ -1,6 +1,6 @@
-# name : ${ ...  } field
-# contributor : joaotavora
-# key : $f
+# name: ${ ...  } field
+# contributor: joaotavora
+# key: $f
 # key: field
 # --
 \${${1:${2:n}:}$3${4:\$(${5:lisp-fn})}\}$0