build: add eslint --cache file

Currently, doing a `git commit` is a bit low, as eslint runs before
the commit.

Adding an `eslint --cache` makes it slightly faster.
On my PC, `git commit` currently is `Done in 12.24s.`

However, after adding this cache file, it is `Done in 7.54s.`,
so about 1.6x faster.

.gitignore

@@ -22,4 +22,7 @@ Gemfile.lock
 /.vs
 
 cypress/screenshots/
-cypress/snapshots/
+cypress/snapshots/
+
+# eslint --cache file
+.eslintcache

package.json

@@ -27,7 +27,7 @@
     "postbuild": "documentation build src/mermaidAPI.js src/config.js src/defaultConfig.js --shallow -f md --markdown-toc false > docs/Setup.md",
     "build:watch": "yarn build:development --watch",
     "release": "yarn build",
-    "lint": "eslint ./ --ext .js,.json,.html,.md",
+    "lint": "eslint --cache ./ --ext .js,.json,.html,.md",
     "lint:fix": "yarn lint --fix",
     "e2e:depr": "yarn lint && jest e2e --config e2e/jest.config.js",
     "cypress": "cypress run",