fix: upgrade @material-ui/core from 4.9.5 to 4.9.7

Snyk has created this PR to upgrade @material-ui/core from 4.9.5 to 4.9.7.

See this package in NPM:
https://www.npmjs.com/package/@material-ui/core

See this project in Snyk:
https://app.snyk.io/org/coderbyheart/project/0f5e54aa-af48-4831-a4d0-f7118aeba5ef?utm_source=github&utm_medium=upgrade-pr

package.json

@@ -15,7 +15,7 @@
     "url": "https://github.com/ausgaben/web"
   },
   "dependencies": {
-    "@material-ui/core": "^4.9.5",
+    "@material-ui/core": "^4.9.7",
     "@material-ui/icons": "^4.9.1",
     "@sentry/browser": "^5.14.1",
     "apollo-cache-inmemory": "^1.6.5",