add missing comma

Author: tbrowder

doc/Language/hashmap.pod6

@@ -405,7 +405,7 @@ Note that the order of the keys and values printed cannot be relied upon; the
 elements of a hash are not always stored the same way in memory for different
 runs of the same program. In fact, since version 2018.05, the order is
 guaranteed to be different in every invocation.  Sometimes one wishes to process
-the elements sorted on, e.g. the keys of the hash. If one wishes to print the
+the elements sorted on, e.g., the keys of the hash. If one wishes to print the
 list of vowels in alphabetical order then one would write
 
     my %vowels = 'a' => 1, 'e' => 2, 'i' => 3, 'o' => 4, 'u' => 5;