Syntax: Fix missing meta.string.yaml scope

Signed-off-by: Jack Cherng <jfcherng@gmail.com>

Author: jfcherng

Package/Sublime Text Syntax Definition/Sublime Text Syntax Definition.sublime-syntax

@@ -623,6 +623,7 @@ contexts:
     - match: "'"
       scope: punctuation.definition.string.begin.yaml
       push:
+        - meta_scope: meta.string.yaml
         - meta_content_scope: source.regexp.oniguruma
         - match: "'(?!')"
           scope: punctuation.definition.string.end.yaml

Package/Sublime Text Syntax Definition/syntax_test_sublime-syntax.yaml

@@ -63,6 +63,7 @@ variables:
 
 
   x9: '{{im_a_variable}}'
+#     ^^^^^^^^^^^^^^^^^^^ meta.string.yaml
 #      ^^^^^^^^^^^^^^^^^ meta.variable.sublime-syntax keyword.other.variable.sublime-syntax
 #        ^^^^^^^^^^^^^ variable.other.sublime-syntax