Fix typo in comment.

Sandro Santilli

src/backend/commands/extension.c

@@ -876,7 +876,7 @@ execute_extension_script(Oid extensionOid, ExtensionControlFile *control,
 
 		/*
 		 * If it's not relocatable, substitute the target schema name for
-		 * occcurrences of @extschema@.
+		 * occurrences of @extschema@.
 		 *
 		 * For a relocatable extension, we needn't do this.  There cannot be
 		 * any need for @extschema@, else it wouldn't be relocatable.