reinstate cross-env

dev_mode/package.json

@@ -87,6 +87,7 @@
   },
   "devDependencies": {
     "@jupyterlab/buildutils": "^1.0.1",
+    "cross-env": "^5.2.0",
     "css-loader": "~2.1.1",
     "duplicate-package-checker-webpack-plugin": "^3.0.0",
     "file-loader": "~3.0.1",

yarn.lock

@@ -3839,6 +3839,14 @@ create-react-context@<=0.2.2:
     fbjs "^0.8.0"
     gud "^1.0.0"
 
+cross-env@^5.2.0:
+  version "5.2.0"
+  resolved "https://registry.yarnpkg.com/cross-env/-/cross-env-5.2.0.tgz#6ecd4c015d5773e614039ee529076669b9d126f2"
+  integrity sha512-jtdNFfFW1hB7sMhr/H6rW1Z45LFqyI431m3qU6bFXcQ3Eh7LtBuG3h74o7ohHZ3crrRkkqHlo4jYHFPcjroANg==
+  dependencies:
+    cross-spawn "^6.0.5"
+    is-windows "^1.0.0"
+
 cross-spawn@^5.0.1:
   version "5.1.0"
   resolved "https://registry.yarnpkg.com/cross-spawn/-/cross-spawn-5.1.0.tgz#e8bd0efee58fcff6f8f94510a0a554bbfa235449"
@@ -6593,7 +6601,7 @@ is-utf8@^0.2.0:
   resolved "https://registry.yarnpkg.com/is-utf8/-/is-utf8-0.2.1.tgz#4b0da1442104d1b336340e80797e865cf39f7d72"
   integrity sha1-Sw2hRCEE0bM2NA6AeX6GXPOffXI=
 
-is-windows@^1.0.1, is-windows@^1.0.2:
+is-windows@^1.0.0, is-windows@^1.0.1, is-windows@^1.0.2:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/is-windows/-/is-windows-1.0.2.tgz#d1850eb9791ecd18e6182ce12a30f396634bb19d"
   integrity sha512-eXK1UInq2bPmjyX6e3VHIzMLobc4J94i4AWn+Hpq3OU5KkrRC96OAcR3PRJ/pGu6m8TRnBHP9dkXQVsT/COVIA==