Use ~ version range for prettier

Author: papandreou

package.json

@@ -40,7 +40,7 @@
     "lodash.unescape": "^4.0.1",
     "mocha": "^6.1.4",
     "offline-github-changelog": "^1.2.0",
-    "prettier": "^1.15.3",
+    "prettier": "~1.19.1",
     "serve": "^11.0.0",
     "unexpected": "^11.0.0",
     "unexpected-documentation-site-generator": "^6.1.0",