PLT-3149 Remove duplicate match-at dependency in package.json (#3195)

webapp/package.json

@@ -19,7 +19,6 @@
     "marked": "mattermost/marked#2d92082cd542dc0adc175a1407194f6a4c3cb621",
     "match-at": "0.1.0",
     "mattermost": "mattermost/mattermost-javascript#master",
-    "match-at": "0.1.0",
     "object-assign": "4.1.0",
     "perfect-scrollbar": "0.6.11",
     "react": "15.0.2",