build: change mermaid live preview to use pnpm

Right now, the netlify build seems to be failing since we're ignoring
the `mermaid-live-editor` lockfile.

This is causing errors with broken dependencies.

Switching to `pnpm`, which the `mermaid-live-editor` uses, fixes these
issues!

scripts/editor.bash

@@ -11,7 +11,6 @@ pushd packages/mermaid
 # Append commit hash to version
 jq ".version = .version + \"+${COMMIT_REF:0:7}\"" package.json > package.tmp.json
 mv package.tmp.json package.json
-yarn link
 popd
 
 pnpm run -r clean
@@ -26,13 +25,14 @@ cd mermaid-live-editor
 git clean -xdf
 rm -rf docs/
 
-# We have to use npm instead of yarn because it causes trouble in netlify
+# Tells PNPM that mermaid-live-editor is not part of this workspace
+touch pnpm-workspace.yaml
+
 # Install dependencies
-yarn install
+pnpm install --frozen-lockfile
 
 # Link local mermaid to live editor
-yarn link mermaid     
+pnpm link ../packages/mermaid
 
 # Force Build the site
-yarn run build
-
+pnpm run build