lintian: Add explicit source format

Change-Id: I935bc05b4fb45be01281be8489f98a74a97faca7
(cherry picked from commit b1fa438ed6c51fc953a63f279fa4dfbd2d7c0cfe)
diff --git a/debian/source/format b/debian/source/format
new file mode 100644
index 0000000..d3827e7
--- /dev/null
+++ b/debian/source/format
@@ -0,0 +1 @@
+1.0