Minor refinement to the summary list items

Summary appears to have been complete sentences that were broken into a numbered list. This modification cleans up the remaining commas and an extra "and".

semver.md

@@ -6,10 +6,10 @@ Summary
 
 Given a version number MAJOR.MINOR.PATCH, increment the:
 
-1. MAJOR version when you make incompatible API changes,
+1. MAJOR version when you make incompatible API changes
 1. MINOR version when you add functionality in a backwards compatible
-   manner, and
-1. PATCH version when you make backwards compatible bug fixes.
+   manner
+1. PATCH version when you make backwards compatible bug fixes
 
 Additional labels for pre-release and build metadata are available as extensions
 to the MAJOR.MINOR.PATCH format.