Bug 1613975 - Mark mozdevice as Rust 2018, r=whimboo,webdriver-reviewers

Differential Revision: https://phabricator.services.mozilla.com/D62210

--HG--
extra : moz-landing-system : lando

testing/mozbase/rust/mozdevice/Cargo.toml

@@ -6,6 +6,7 @@ description = "Client library for the Android Debug Bridge (adb)"
 keywords = ["mozilla", "firefox", "geckoview", "android", "adb"]
 repository = "https://hg.mozilla.org/mozilla-central/file/tip/testing/mozbase/rust/mozdevice"
 license = "MPL-2.0"
+edition = "2018"
 
 [dependencies]
 log = { version = "0.4", features = ["std"] }