Fix / -> \ replacement for windows. Closes #200

Author: dschep

lib/pip.js

@@ -147,7 +147,7 @@ function installRequirements(
  */
 function dockerPathForWin(options, path) {
   if (process.platform === 'win32' && options.dockerizePip) {
-    return path.replace('\\', '/');
+    return path.replace(/\\/g, '/');
   }
   return path;
 }