vendor/golang_org/text/unicode/norm: re-vendor

This picks up just a trivial fix,
making vet (and thus me) happy.

Change-Id: Ib82ae44c081ff1ec5c078196a6cd5e1a3505d03b
Reviewed-on: https://go-review.googlesource.com/32427
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/vendor/golang_org/x/text/unicode/norm/readwriter.go

@@ -112,7 +112,6 @@ func (r *normReader) Read(p []byte) (int, error) {
 			}
 		}
 	}
-	panic("should not reach here")
 }
 
 // Reader returns a new reader that implements Read