.gitignore: Ignore docker source copy

Signed-off-by: Fam Zheng <famz@redhat.com>
diff --git a/.gitignore b/.gitignore
index 88a80ff..38ee1c5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -108,4 +108,5 @@
 cscope.*
 tags
 TAGS
+docker-src.*
 *~