lintian: Add in an explicit source format

Change-Id: Iaba8d2ab7c5a1e2b7507e42bf004e5e7e9c11d3b
(cherry picked from commit 862042d7999c77970056231ddca1a0d585bfd400)
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