Match minerva base styles for Parsoid

* The Minerva repository has a ".mw-ref" style which is Cite-specific
  so that makes be wonder if the expectation is for this to be in
  that file instead. That would be a really simple fix and be attached
  to the rule for sup as an extra selector.

* But, it seems like Cite extension is the right place for this.

* Found while trying to test Cite rendering with MFE.

Notes:
* This mirrors the style added in
Ieb91c1251839ff4bb54451aae69af9fb88322219


Change-Id: Iae1d391ef11e53110bfb758d45a0fbdf2addf62e

extension.json

@@ -62,7 +62,10 @@
 			"localBasePath": "modules/parsoid-styles",
 			"remoteExtPath": "Cite/modules/parsoid-styles",
 			"class": "Cite\\ResourceLoader\\CiteCSSFileModule",
-			"styles": "ext.cite.parsoid.styles.less"
+			"styles": "ext.cite.parsoid.styles.less",
+			"skinStyles": {
+				"minerva": "ext.cite.parsoid.styles.minerva.less"
+			}
 		},
 		"ext.cite.visualEditor.core": {
 			"localBasePath": "modules/ve-cite",

modules/parsoid-styles/ext.cite.parsoid.styles.minerva.less

@@ -0,0 +1,5 @@
+/* Match sup style in Minerva's skins.minerva.base.styles/content/text.less */
+span[ rel='mw:referencedBy' ] > a::before {
+	font-size: 0.75em;
+	line-height: 1; // redundant but matching declarations in minerva codebase
+}