go spec: adjust language for constant typing

Fixes #1421.

R=r, rsc, iant, ken2
CC=golang-dev
https://golang.org/cl/4039042

doc/go_spec.html

@@ -561,7 +561,7 @@ or <a href="#Conversions">conversion</a>, or implicitly when used in a
 <a href="#Assignments">assignment</a> or as an
 operand in an <a href="#Expressions">expression</a>.
 It is an error if the constant value
-cannot be accurately represented as a value of the respective type.
+cannot be represented as a value of the respective type.
 For instance, <code>3.0</code> can be given any integer or any
 floating-point type, while <code>2147483648.0</code> (equal to <code>1&lt;&lt;31</code>)
 can be given the types <code>float32</code>, <code>float64</code>, or <code>uint32</code> but