Update for the 1.18 release

Author: alexcrichton

_config.yml

@@ -1,18 +1,18 @@
 name: The Rust Programming Language
-stable: "1.17.0"
-stable_date: "2017-04-27"
-stable_blog: "https://blog.rust-lang.org/2017/04/27/Rust-1.17.html"
-stable_full_version: "rustc 1.17.0 (56124baa9 2017-04-24)"
-beta: "1.18"
-beta_date: "2017-06-08"
-nightly: "1.19"
+stable: "1.18.0"
+stable_date: "2017-06-08"
+stable_blog: "https://blog.rust-lang.org/2017/06/08/Rust-1.18.html"
+stable_full_version: "rustc 1.18.0 (03fc9d622 2017-06-06)"
+beta: "1.19"
+beta_date: "2017-07-20"
+nightly: "1.20"
 channels:
   - name: "stable"
-    vers: "1.17.0"
-    package: "1.17.0"
+    vers: "1.18.0"
+    package: "1.18.0"
   - name: "beta"
-    vers: "1.18"
+    vers: "1.19"
     package: "beta"
   - name: "nightly"
-    vers: "1.19"
+    vers: "1.20"
     package: "nightly"