Update the @openwebwork/pg-codemirror-editor dependency.

The `@openwebwork/pg-codemirror-editor` and its dependency packages
`@openwebwork/codemirror-lang-pg`, `codemirror-lang-perl`, and
`codemirror-lang-mt` have all had all dependencies updated, and the
bracket matching issue reported in
openwebwork/codemirror-lang-pg#1 fixed.

The resulting changes have also been published.

This just updates webwork2's dependency so that those updated packages
can be used by webwork2.

Note, I did take some liberty by pushing the updates for the
`@openwebwork/pg-codemirror-editor` and
`@openwebwork/codemirror-lang-perl` packages without going through the
pull request process.  But with the tiered depencies here that would be
tedious to go through the approval process from bottom to top.

Author: drgrice1