doc/go1.11: add space in Go version name

Missed in CL 124516.

Change-Id: I6488196c8392987d69eca832ab4969aaafe1a26c
Reviewed-on: https://go-review.googlesource.com/124658Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/go1.11.html

@@ -275,7 +275,7 @@ func f(v interface{}) {
   before running, tests that do not typecheck will now fail.
 
   In particular, tests that contain an unused variable inside a
-  closure compiled with Go1.10, because the Go compiler incorrectly
+  closure compiled with Go 1.10, because the Go compiler incorrectly
   accepted them (<a href="https://golang.org/issues/3059">Issue #3059</a>),
   but will now fail, since <code>go/types</code> correctly reports an
   "unused variable" error in this case.