use cross-env to set environment variables in scripts (#121)

When running tests and builds on Windows, `VAR_NAME=value command` is
not valid syntax for setting environment variables. cross-env takes care
of setting variables properly before executing the command.

package-lock.json

@@ -4385,6 +4385,58 @@
         "sha.js": "^2.4.8"
       }
     },
+    "cross-env": {
+      "version": "6.0.3",
+      "resolved": "https://registry.npmjs.org/cross-env/-/cross-env-6.0.3.tgz",
+      "integrity": "sha512-+KqxF6LCvfhWvADcDPqo64yVIB31gv/jQulX2NGzKS/g3GEVz6/pt4wjHFtFWsHMddebWD/sDthJemzM4MaAag==",
+      "dev": true,
+      "requires": {
+        "cross-spawn": "^7.0.0"
+      },
+      "dependencies": {
+        "cross-spawn": {
+          "version": "7.0.1",
+          "resolved": "https://registry.npmjs.org/cross-spawn/-/cross-spawn-7.0.1.tgz",
+          "integrity": "sha512-u7v4o84SwFpD32Z8IIcPZ6z1/ie24O6RU3RbtL5Y316l3KuHVPx9ItBgWQ6VlfAFnRnTtMUrsQ9MUUTuEZjogg==",
+          "dev": true,
+          "requires": {
+            "path-key": "^3.1.0",
+            "shebang-command": "^2.0.0",
+            "which": "^2.0.1"
+          }
+        },
+        "path-key": {
+          "version": "3.1.1",
+          "resolved": "https://registry.npmjs.org/path-key/-/path-key-3.1.1.tgz",
+          "integrity": "sha512-ojmeN0qd+y0jszEtoY48r0Peq5dwMEkIlCOu6Q5f41lfkswXuKtYrhgoTpLnyIcHm24Uhqx+5Tqm2InSwLhE6Q==",
+          "dev": true
+        },
+        "shebang-command": {
+          "version": "2.0.0",
+          "resolved": "https://registry.npmjs.org/shebang-command/-/shebang-command-2.0.0.tgz",
+          "integrity": "sha512-kHxr2zZpYtdmrN1qDjrrX/Z1rR1kG8Dx+gkpK1G4eXmvXswmcE1hTWBWYUzlraYw1/yZp6YuDY77YtvbN0dmDA==",
+          "dev": true,
+          "requires": {
+            "shebang-regex": "^3.0.0"
+          }
+        },
+        "shebang-regex": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/shebang-regex/-/shebang-regex-3.0.0.tgz",
+          "integrity": "sha512-7++dFhtcx3353uBaq8DDR4NuxBetBzC7ZQOhmTQInHEd6bSrXdiEyzCvG07Z44UYdLShWUyXt5M/yhz8ekcb1A==",
+          "dev": true
+        },
+        "which": {
+          "version": "2.0.2",
+          "resolved": "https://registry.npmjs.org/which/-/which-2.0.2.tgz",
+          "integrity": "sha512-BLI3Tl1TW3Pvl70l3yq3Y64i+awpwXqsGBYWkkqMtnbXgrMD+yj7rhW0kuEDxzJaYXGjEW5ogapKNMEKNMjibA==",
+          "dev": true,
+          "requires": {
+            "isexe": "^2.0.0"
+          }
+        }
+      }
+    },
     "cross-spawn": {
       "version": "5.1.0",
       "resolved": "https://registry.npmjs.org/cross-spawn/-/cross-spawn-5.1.0.tgz",

package.json

@@ -14,8 +14,8 @@
     "test": "jest --coverage",
     "test:watch": "jest --watch",
     "doc": "npm run doc:dev",
-    "doc:dev": "NODE_ENV=development parcel website/index.html --out-dir doc --no-cache",
-    "doc:build": "rimraf doc && NODE_ENV=production parcel build website/index.html --out-dir doc --public-url ./ --no-cache --no-source-maps"
+    "doc:dev": "cross-env NODE_ENV=development parcel website/index.html --out-dir doc --no-cache",
+    "doc:build": "rimraf doc && cross-env NODE_ENV=production parcel build website/index.html --out-dir doc --public-url ./ --no-cache --no-source-maps"
   },
   "files": [
     "index.d.ts",
@@ -61,6 +61,7 @@
     "bannerjs": "^1.0.5",
     "classnames": "^2.2.5",
     "colors-cli": "^1.0.26",
+    "cross-env": "^6.0.3",
     "eslint": "^4.19.1",
     "eslint-config-airbnb": "^16.1.0",
     "eslint-plugin-import": "^2.18.2",