Fix return type of WebAssembly.Table.set method.
In externs file, function without any return type are considered to return an unknown type. According to the spec, Table.set() returns undefined.
@@ -171,5 +171,6 @@ WebAssembly.Table.prototype.get = function(index) {};
/**
* @param {number} index
* @param {?TableFunction} value
+ * @return {undefined}
*/
WebAssembly.Table.prototype.set = function(index, value) {};
