fix: plugins/graphiql/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-WEBPACKDEVSERVER-10300775
- https://snyk.io/vuln/SNYK-JS-WEBPACKDEVSERVER-10300777
- https://snyk.io/vuln/SNYK-JS-TARFS-10293725

Author: snyk-bot

plugins/graphiql/package.json

@@ -34,7 +34,7 @@
   "dependencies": {
     "@backstage/core-components": "workspace:^",
     "@backstage/core-plugin-api": "workspace:^",
-    "@backstage/theme": "workspace:^",
+    "@backstage/theme": "0.1.1",
     "@material-ui/core": "^4.12.2",
     "@material-ui/icons": "^4.9.1",
     "@material-ui/lab": "4.0.0-alpha.61",