Fix npm@6 warnings about deprecated "prepublish" (#1340)

package.json

@@ -38,7 +38,7 @@
     "build:mjs": "BABEL_MODULES=1 babel src --optional runtime --ignore __tests__ --out-dir dist/module/ && for file in $(find dist/module -name '*.js'); do mv \"$file\" `echo \"$file\" | sed 's/dist\\/module/dist/g; s/.js$/.mjs/g'`; done && rm -rf dist/module",
     "build:flow": "for file in $(find ./src -name '*.js' -not -path '*/__tests__*'); do cp \"$file\" `echo \"$file\" | sed 's/\\/src\\//\\/dist\\//g'`.flow; done",
     "preversion": ". ./resources/checkgit.sh && npm test",
-    "prepublish": ". ./resources/prepublish.sh",
+    "prepublishOnly": ". ./resources/prepublish.sh",
     "gitpublish": ". ./resources/gitpublish.sh"
   },
   "dependencies": {

resources/prepublish.sh

@@ -1,10 +1,3 @@
-# Because of a long-running npm issue (https://github.com/npm/npm/issues/3059)
-# prepublish runs after `npm install` and `npm pack`.
-# In order to only run prepublish before `npm publish`, we have to check argv.
-if node -e "process.exit(($npm_config_argv).original.length > 0 && ($npm_config_argv).original[0].indexOf('pu') === 0)"; then
-  exit 0;
-fi
-
 # Publishing to NPM is currently supported by Travis CI, which ensures that all
 # tests pass first and the deployed module contains the correct file structure.
 # In order to prevent inadvertently circumventing this, we ensure that a CI