[clang-format][docs] Fix invalid CSS syntax in versionbadge

[rymiel]

Summary

CSS uses colons, not the equals sign. The final semicolon is optional,
but preferred to be included. Really, the font property doesn't really
need to be there, but I suppose it was put there for a reason.

It's surprising how lenient browsers are when parsing

clang/docs/ClangFormatStyleOptions.rst

 .. raw:: html
 
       <style type="text/css">
-        .versionbadge { background-color: #1c913d; height: 20px; display: inline-block; width: 120px; text-align: center; border-radius: 5px; color: #FFFFFF; font-family="Verdana,Geneva,DejaVu Sans,sans-serif" }
+        .versionbadge { background-color: #1c913d; height: 20px; display: inline-block; width: 120px; text-align: center; border-radius: 5px; color: #FFFFFF; font-family: "Verdana,Geneva,DejaVu Sans,sans-serif"; }
       </style>
 
 .. role:: versionbadge
 
 ==========================
 Clang-Format Style Options
 ==========================