"statement tree" -> "statement node".

Fix #967.

Author: munificent

book/statements-and-state.md

@@ -405,7 +405,7 @@ That `IDENTIFIER` clause matches a single identifier token, which is understood
 to be the name of the variable being accessed.
 
 These new grammar rules get their corresponding syntax trees. Over in the AST
-generator, we add a <span name="var-stmt-ast">new statement</span> tree for a
+generator, we add a <span name="var-stmt-ast">new statement</span> node for a
 variable declaration.
 
 ^code var-stmt-ast (1 before, 1 after)

site/statements-and-state.html

@@ -568,7 +568,7 @@ <h3><a href="#variable-syntax" name="variable-syntax"><small>8&#8202;.&#8202;2&#
 <p>That <code>IDENTIFIER</code> clause matches a single identifier token, which is understood
 to be the name of the variable being accessed.</p>
 <p>These new grammar rules get their corresponding syntax trees. Over in the AST
-generator, we add a <span name="var-stmt-ast">new statement</span> tree for a
+generator, we add a <span name="var-stmt-ast">new statement</span> node for a
 variable declaration.</p>
 <div class="codehilite"><pre class="insert-before">
       &quot;Expression : Expr expression&quot;,