doc: fix typo in go 1.1 doc

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/7725049

doc/go1.1.html

@@ -495,7 +495,7 @@ and
 <a href="/pkg/reflect/#SliceOf"><code>SliceOf</code></a>
 construct new
 <a href="/pkg/reflect/#Type"><code>Types</code></a>
-from existing types, for example to construct a the type <code>[]T</code> given
+from existing types, for example to construct the type <code>[]T</code> given
 only <code>T</code>.
 </p>