use 'tree-ish' instead of 'treeish'

Replace 'treeish' in documentation and comments with 'tree-ish' to
match gitglossary(7).

The only remaining instances of 'treeish' are:
  * variable, function, and macro names
  * "(also treeish)" in the definition of tree-ish in gitglossary(7)

Signed-off-by: Richard Hansen <rhansen@bbn.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/git-cvsserver.perl b/git-cvsserver.perl
index a0d796e..a9f6f8e 100755
--- a/git-cvsserver.perl
+++ b/git-cvsserver.perl
@@ -4338,7 +4338,7 @@
 =head2 getRevisionDirMap
 
 A "revision dir map" contains all the plain-file filenames associated
-with a particular revision (treeish), organized by directory:
+with a particular revision (tree-ish), organized by directory:
 
   $type = $out->{$dir}{$fullName}