Fix two formatting issues on Contributing page (#77)

https://yargs.js.org/contributing/ had two visible issues:

- There was a space before the comma in “Create a new issue , or comment on an existing issue”. This was due to the practice of writing all `a` elements with inner spaces. I removed all such inner spaces to avoid this problem in the future.
- There was an unnecessary comma after a sentence: “write code. ,”

I also deeleted some unnecessary blank lines at the bottom.

Co-authored-by: Benjamin E. Coe <[email protected]>

Author: roryokane

contributing/index.html

@@ -24,7 +24,7 @@
       <li> Look through the existing issues and see if your idea is something new. </li>
       <li> Create a <a href="https://github.com/yargs/yargs/issues">new issue</a>, or comment on an existing issue that you would like to help solve:
         <ul>
-          <li> it's usually best to get some feedback before proceeding to write code. ,</li>
+          <li> it's usually best to get some feedback before proceeding to write code.</li>
         </ul>
       </li>
 
@@ -107,8 +107,6 @@
 
     <p class="description">
       This Code of Conduct is adapted from the <a href="http://contributor-covenant.org">Contributor Covenant</a>, version 1.3.0, available at <a href="http://contributor-covenant.org/version/1/3/0/">http://contributor-covenant.org/version/1/3/0/</a>
-
-
     </p>
 
   </div>