Fix missing comma in tower-rate-limit Error impl (#58)

This should de-break the build. However, I'm concerned that this made it pass CI --- we should fix the Travis configs.

tower-rate-limit/src/lib.rs

@@ -183,9 +183,8 @@ where
 {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            Error::Upstream(ref why) => fmt::Display::fmt(why, f)
-            Error::NoCapacity =>
-                write!(f, "rate limit exceeded"),
+            Error::Upstream(ref why) => fmt::Display::fmt(why, f),
+            Error::NoCapacity => f.pad("rate limit exceeded"),
         }
     }
 }