fix(core): pin material-table to fix e2e CI errors in master

This PR https://github.com/mbrn/material-table/pull/2311 broke material-table builds that use webpack. We don't see the problem locally since we have the unaffected version in our lockfiles. However when running the e2e (app generation) flows, there is no lockfile so it resolves to the affected broken versions, breaking master builds at the moment.

Pinning to the unaffected version for now.

packages/core/package.json

@@ -40,7 +40,7 @@
     "classnames": "^2.2.6",
     "clsx": "^1.1.0",
     "lodash": "^4.17.15",
-    "material-table": "1.68.x",
+    "material-table": "1.68.0",
     "prop-types": "^15.7.2",
     "rc-progress": "^3.0.0",
     "react": "^16.12.0",

yarn.lock

@@ -15310,7 +15310,7 @@ markdown-toc@^1.2.0:
     repeat-string "^1.6.1"
     strip-color "^0.1.0"
 
-material-table@1.68.x:
+material-table@1.68.0:
   version "1.68.0"
   resolved "https://registry.npmjs.org/material-table/-/material-table-1.68.0.tgz#275c3d9a885c40ae4bc5a7461c00e877f92397b9"
   integrity sha512-dyJJaVsS3m+i6sn71AvYcVdA1P9X1XiUOM2PekfvEeeMtkdQb66oChGkk77ndYi3Ja6j4DovGVNrgeVLwXLZiw==