fix: upgrade aws-amplify from 3.0.18 to 3.0.20 (#109)

Snyk has created this PR to upgrade aws-amplify from 3.0.18 to 3.0.20.

See this package in NPM:
https://www.npmjs.com/package/aws-amplify

See this project in Snyk:
https://app.snyk.io/org/johanneskonings/project/b30410ce-f052-409e-904e-a2e4798c61db?utm_source=github&utm_medium=upgrade-pr

package.json

@@ -13,7 +13,7 @@
     "@material-ui/core": "4.11.0",
     "@material-ui/icons": "4.9.1",
     "@material-ui/pickers": "^3.2.10",
-    "aws-amplify": "^3.0.18",
+    "aws-amplify": "^3.0.20",
     "chartist": "0.11.4",
     "classnames": "2.2.6",
     "date-fns": "^2.14.0",