Run rustfmt on selectors, servo_arc, and style.

This was generated with:

./mach cargo fmt --package selectors &&
./mach cargo fmt --package servo_arc &&
./mach cargo fmt --package style

Using rustfmt 0.4.1-nightly (a4462d1 2018-03-26)

components/style/values/computed/time.rs

@@ -18,9 +18,7 @@ pub struct Time {
 impl Time {
     /// Creates a time value from a seconds amount.
     pub fn from_seconds(seconds: CSSFloat) -> Self {
-        Time {
-            seconds: seconds,
-        }
+        Time { seconds: seconds }
     }
 
     /// Returns `0s`.