Add variations on start and build scripts for Windows systems (#155)

* Add variations on start and build scripts for Windows systems

These scripts set an environment variable before invoking
react-app-rewired. The syntax for doing this is different on Windows
systems. Two new scripts are defined to make these actions available to
Windows users.

* Use cross-env to support start and build tasks on Mac, Windows, and Linux

---------

Co-authored-by: Chris Moesel <cmoesel@mitre.org>

package.json

@@ -28,6 +28,7 @@
   },
   "devDependencies": {
     "cors": "^2.8.5",
+    "cross-env": "^7.0.3",
     "eslint-config-prettier": "^6.11.0",
     "eslint-plugin-prettier": "^3.1.3",
     "express": "^4.18.2",
@@ -50,8 +51,8 @@
     }
   },
   "scripts": {
-    "start": "NODE_OPTIONS=--openssl-legacy-provider react-app-rewired start",
-    "build": "NODE_OPTIONS=--openssl-legacy-provider react-app-rewired build",
+    "start": "cross-env NODE_OPTIONS=--openssl-legacy-provider react-app-rewired start",
+    "build": "cross-env NODE_OPTIONS=--openssl-legacy-provider react-app-rewired build",
     "serve-build": "node scripts/serve-build.js",
     "lint": "eslint \"./src/**/*.js\"",
     "lint-fix": "eslint \"./src/**/*.js\" --fix",