Editorial: Insert blank line between productions (#2129)

(re PR #1948)

Author: jmdyck

spec.html

@@ -26758,6 +26758,7 @@ <h1>Function.prototype.toString ( )</h1>
         <emu-grammar type="definition">
           NativeFunction :
             `function` NativeFunctionAccessor? PropertyName[~Yield, ~Await]? `(` FormalParameters[~Yield, ~Await] `)` `{` `[` `native` `code` `]` `}`
+
           NativeFunctionAccessor :
             `get`
             `set`