Use a more specific scope for heredoc folding

This prevents strings that are not heredocs from being foldable.

Author: matteocoder

Fold.tmPreferences

@@ -23,9 +23,17 @@
             </dict>
             <dict>
                 <key>begin</key>
-                <string>punctuation.definition.string.begin</string>
+                <string>string.quoted.double.heredoc punctuation.definition.string.begin</string>
                 <key>end</key>
-                <string>punctuation.definition.string.end</string>
+                <string>string.quoted.double.heredoc punctuation.definition.string.end</string>
+                <key>excludeTrailingNewlines</key>
+                <false/>
+            </dict>
+            <dict>
+                <key>begin</key>
+                <string>string.quoted.single.heredoc punctuation.definition.string.begin</string>
+                <key>end</key>
+                <string>string.quoted.single.heredoc punctuation.definition.string.end</string>
                 <key>excludeTrailingNewlines</key>
                 <false/>
             </dict>