Update create-mongodb-nodejs.md

Create folder command on bash is "mkdir" instead of "md".

Author: kuniteru

articles/cosmos-db/create-mongodb-nodejs.md

@@ -51,7 +51,7 @@ Run the following commands to clone the sample repository. This sample repositor
 1. Open a command prompt, create a new folder named git-samples, then close the command prompt.
 
     ```bash
-    md "C:\git-samples"
+    mkdir "C:\git-samples"
     ```
 
 2. Open a git terminal window, such as git bash, and use the `cd` command to change to the new folder to install the sample app.