spec: delete spurious space (missed fix from previous review)

No semantic change.

R=rsc
CC=golang-dev
https://golang.org/cl/2099041

doc/go_spec.html

@@ -1907,7 +1907,7 @@ argument.  For instance, the method <code>Scale</code> has type
 </p>
 
 <pre>
-func (p *Point, factor float)
+func(p *Point, factor float)
 </pre>
 
 <p>