update readme.md

Author: leo6104

README.md

@@ -608,7 +608,7 @@ If your [electron-rebuild step is failing](https://github.com/ipfs/js-ipfs/issue
 
 ```bash
 # Electron's version.
-export npm_config_target=1.7.6
+export npm_config_target=2.0.0
 # The architecture of Electron, can be ia32 or x64.
 export npm_config_arch=x64
 export npm_config_target_arch=x64