Update RAKUDO_HIST's default value

Author: stoned

doc/Programs/03-environment-variables.pod6

@@ -105,7 +105,9 @@ X<|RAKUDO_HIST>
 =item C<RAKUDO_HIST>
 
 This specifies the location of the history file used by the
-line editor; the default is C<~/.perl6/rakudo-history>.
+line editor; the default is C<~/.raku/rakudo-history>.
+Before Rakudo version 2020.02 the default was
+C<~/.perl6/rakudo-history>.
 
 =head2 Other