feat(template): issue template look better (angular#2384)

The current template produces disjunct list items so the numbering contains only 1's. Let's make this a H3

Author: clemens-tolboom

.github/ISSUE_TEMPLATE.md

@@ -1,22 +1,23 @@
 > Please provide us with the following information:
 > ---------------------------------------------------------------
 
-1. OS?  Windows 7, 8 or 10. Linux (which distribution). Mac OSX (Yosemite? El Capitan?)
+### OS?
+> Windows 7, 8 or 10. Linux (which distribution). Mac OSX (Yosemite? El Capitan?)
 
 
-2. Versions. Please run `ng --version`. If there's nothing outputted, please run
-in a Terminal: `node --version` and paste the result here:
+### Versions.
+> Please run `ng --version`. If there's nothing outputted, please run in a Terminal: `node --version` and paste the result here:
 
 
-3. Repro steps. Was this an app that wasn't created using the CLI? What change did you
-   do on your code? etc.
+### Repro steps.
+> Was this an app that wasn't created using the CLI? What change did you do on your code? etc.
 
 
-4. The log given by the failure. Normally this include a stack trace and some
-   more information.
+### The log given by the failure.
+> Normally this include a stack trace and some more information.
 
 
-5. Mention any other details that might be useful.
+### Mention any other details that might be useful.
 
 > ---------------------------------------------------------------
 > Thanks! We'll be in touch soon.