spec: slight wording change to remove a formal contradiction

Fixes #4324.

R=r
CC=golang-dev
https://golang.org/cl/6822062

doc/go_spec.html

@@ -2128,13 +2128,13 @@ For struct literals the following rules apply:
 <ul>
 	<li>A key must be a field name declared in the LiteralType.
 	</li>
-	<li>A literal that does not contain any keys must
+	<li>An element list that does not contain any keys must
 	    list an element for each struct field in the
 	    order in which the fields are declared.
 	</li>
 	<li>If any element has a key, every element must have a key.
 	</li>
-	<li>A literal that contains keys does not need to
+	<li>An element list that contains keys does not need to
 	    have an element for each struct field. Omitted fields
 	    get the zero value for that field.
 	</li>