lintian: Add in an explicit source format

Change-Id: Ic1a2e96a38e31836b63dfddbfe3004e349559a16
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