run-script: Do not use SET to fetch the env in git-bash or cygwin

Credit: @gucong3000
PR-URL: npm/npm#19418
Reviewed-By: @iarna

lib/run-script.js

@@ -9,6 +9,7 @@ var chain = require('slide').chain
 var usage = require('./utils/usage')
 var output = require('./utils/output.js')
 var didYouMean = require('./utils/did-you-mean')
+var isWindowsShell = require('./utils/is-windows-shell.js')
 
 runScript.usage = usage(
   'run-script',
@@ -139,7 +140,7 @@ function run (pkg, wd, cmd, args, cb) {
       if (cmd === 'test') {
         pkg.scripts.test = 'echo \'Error: no test specified\''
       } else if (cmd === 'env') {
-        if (process.platform === 'win32') {
+        if (isWindowsShell) {
           log.verbose('run-script using default platform env: SET (Windows)')
           pkg.scripts[cmd] = 'SET'
         } else {

lib/utils/is-windows-bash.js

@@ -1,3 +1,4 @@
 'use strict'
 var isWindows = require('./is-windows.js')
-module.exports = isWindows && /^MINGW(32|64)$/.test(process.env.MSYSTEM)
+module.exports = isWindows &&
+  (/^MINGW(32|64)$/.test(process.env.MSYSTEM) || process.env.TERM === "cygwin")