fix mime types data (#23226)

generated via https://github.com/bung87/mimetypes_gen

source data:
http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/conf/mime.types?view=co

tests/stdlib/tmimetypes.nim

@@ -11,8 +11,11 @@ template main() =
   var m = newMimetypes()
   doAssert m.getMimetype("mp4") == "video/mp4"
   doAssert m.getExt("application/json") == "json"
+  doAssert m.getMimetype("json") == "application/json"
   m.register("foo", "baa")
   doAssert m.getMimetype("foo") == "baa"
+  doAssert m.getMimetype("txt") == "text/plain"
+  doAssert m.getExt("text/plain") == "txt"
   # see also `runnableExamples`.
   # xxx we should have a way to avoid duplicating code between runnableExamples and tests