lexer: Remove match-at dependency, use RegExp (#1447)

* lexer: Remove `match-at` dependency, use RegExp

* chore(package): update flow-bin to version 0.75.0

* Fix flow error

* Remove unused flow libs

* Minor fix

* Throw an error when `RegExp.exec` jumps

package.json

@@ -30,7 +30,7 @@
     "eslint": "^5.0.0",
     "eslint-plugin-flowtype": "^2.40.1",
     "file-loader": "^1.1.11",
-    "flow-bin": "^0.74.0",
+    "flow-bin": "^0.75.0",
     "husky": "^1.0.0-rc.8",
     "jest": "^23.0.1",
     "jest-serializer-html": "^5.0.0",
@@ -80,7 +80,6 @@
     "dist:dist": "rimraf dist/ && cp -r build/katex/ dist/"
   },
   "dependencies": {
-    "match-at": "^0.1.1",
     "nomnom": "^1.8.1"
   },
   "husky": {