environ: simplify description of GIT_INDEX_FILE

Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

Documentation/git.txt

@@ -455,7 +455,7 @@ is worth noting that they may be used/overridden by SCMS sitting above
 Git so take care if using a foreign front-end.
 
 `GIT_INDEX_FILE`::
-	This environment allows the specification of an alternate
+	This environment variable specifies an alternate
 	index file. If not specified, the default of `$GIT_DIR/index`
 	is used.