Update rss crate version dependency

Also bump this crate's version to 0.2.0, because rss's types are exposed
in syndication's public API, which will force clients to update rss if
they depend on it and if they need to interoperate with syndication to
update.

[breaking-change]

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "syndication"
-version = "0.1.1"
+version = "0.2.0"
 authors = ["Tom Shen <[email protected]>"]
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/tomshen/rust-syndication"
@@ -10,4 +10,4 @@ exclude = ["test-data/*"]
 
 [dependencies]
 atom_syndication = "0.1"
-rss = "0.2"
+rss = "0.3"