lib: adding keep-alive header to download requests

PR-URL: #1863
Reviewed-By: Rod Vagg <[email protected]>
Reviewed-By: Richard Lau <[email protected]>

Author: Milad Farazmand

lib/install.js

@@ -391,7 +391,8 @@ function download (gyp, env, url) {
   var requestOpts = {
     uri: url,
     headers: {
-      'User-Agent': 'node-gyp v' + gyp.version + ' (node ' + process.version + ')'
+      'User-Agent': 'node-gyp v' + gyp.version + ' (node ' + process.version + ')',
+      'Connection': 'keep-alive'
     }
   }