v.js: fix strings.Builder

vlib/strings/builder_c.v

@@ -13,7 +13,7 @@ pub:
 
 pub fn new_builder(initial_size int) Builder {
 	return Builder {
-		// buf: _make(0, initial_size, sizeof(byte))
+		buf: _make(0, initial_size, sizeof(byte))
 	}
 }
 

vlib/strings/builder_js.v

@@ -0,0 +1,31 @@
+// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+
+module strings
+
+struct Builder {
+pub:
+	len int
+}
+
+pub fn new_builder(initial_size int) Builder {
+	return Builder {
+	}
+}
+
+pub fn (b mut Builder) write(s string) {
+}
+
+pub fn (b mut Builder) writeln(s string) {
+}
+
+pub fn (b Builder) str() string {
+	return ''
+}
+
+pub fn (b mut Builder) cut(n int) {
+}
+
+pub fn (b mut Builder) free() {
+}