webdriver: Update version number for release

Source-Repo: https://github.com/mozilla/webdriver-rust
Source-Revision: 0bb4f061dea2e22cdff95859575d7461a5aa36f0

--HG--
extra : subtree_source : http%3A//tristan.corp.lon2.mozilla.com%3A8000
extra : subtree_revision : bd34ee4b415de1efafb3a66313e82d6db5b7ef7a

testing/webdriver/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 
 name = "webdriver"
-version = "0.17.1"
+version = "0.18.0"
 authors = ["Mozilla Tools and Automation <auto-tools@mozilla.com>"]
 description = "Library implementing the wire protocol for the W3C WebDriver specification."
 repository = "https://github.com/jgraham/webdriver-rust"