Add json_test to gitignore (Hirohito Higashi)
diff --git a/.gitignore b/.gitignore
index acd9fc8..97e6d2d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -78,3 +78,4 @@
 src/testdir/messages
 src/testdir/viminfo
 src/memfile_test
+src/json_test