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/selectors/visitor.rs

@@ -38,9 +38,7 @@ pub trait SelectorVisitor {
     ///
     /// Gets the combinator to the right of the selector, or `None` if the
     /// selector is the rightmost one.
-    fn visit_complex_selector(&mut self,
-                              _combinator_to_right: Option<Combinator>)
-                              -> bool {
+    fn visit_complex_selector(&mut self, _combinator_to_right: Option<Combinator>) -> bool {
         true
     }
 }