Bug 1477883: Update itoa. r=me

Has been updated in servo for a long time, and we already have the new version
in tree.

MozReview-Commit-ID: 1yNOsqwLign

servo/components/style/Cargo.toml

@@ -40,7 +40,7 @@ fnv = "1.0"
 hashglobe = { path = "../hashglobe" }
 html5ever = {version = "0.22", optional = true}
 itertools = "0.7.6"
-itoa = "0.3"
+itoa = "0.4"
 lazy_static = "1"
 log = "0.4"
 malloc_size_of = { path = "../malloc_size_of" }