bump version.bzl to 1.3 (#1062)

Time for a rollup release of fixes, before we switch to depending on the
other repo for providers.
diff --git a/version.bzl b/version.bzl
index 0750659..283355e 100644
--- a/version.bzl
+++ b/version.bzl
@@ -13,4 +13,4 @@
 # limitations under the License.
 """The version of rules_pkg."""
 
-version = "1.2.0"
+version = "1.3.0"