Update issue template to include MacOS and reformat.

Author: david-cattermole

docs/ISSUE_TEMPLATE.md

@@ -1,4 +1,4 @@
-### Problem / Feature
+### Problem or Feature
 <!-- Describe the problem or suggestion here. Be specific about your problem. -->
 
 **Expected behavior:**
@@ -17,8 +17,7 @@
 <!-- What software and hardware versions are you running?
 -->
 
-- mmSolver version:
-[mmSolver version number here]
+- mmSolver version: [mmSolver version number here]
 
 - Maya version:
 <!-- What Maya version are you using?
@@ -36,6 +35,4 @@ print 'GPU:', ''.join(maya.cmds.ogs(deviceInformation=True))
 
 [Maya version number or print out here]
 
-- Operating System (OS):
-<!-- Windows or Linux?
--->
+- Operating System (OS): <!-- Windows, Linux and MacOS -->