fix typo: DEPTH_BUFFER_BITS => DEPTH_BUFFER_BIT (WebGLSamples#165)

* fix typo: DEPTH_BUFFER_BITS => DEPTH_BUFFER_BIT

* add clear depth buffer for demo 'glsl_flat_smooth_interpolators'

Co-authored-by: stevecai <stevecai@tencent.com>

Author: little-csd

Diff for: samples/glsl_flat_smooth_interpolators.html

@@ -260,7 +260,7 @@
             // -- Render loop
             (function render() {
                 gl.clearColor(0.0, 0.0, 0.0, 1.0);
-                gl.clear(gl.COLOR_BUFFER_BIT);
+                gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
 
                 mat4.rotateY(modelView, modelView, rotatationSpeedY);
 

Diff for: samples/query_occlusion.html

@@ -95,7 +95,7 @@
 
         // -- Render
         gl.clearColor(0.0, 0.0, 0.0, 1.0);
-        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BITS);
+        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
 
         gl.bindVertexArray(vertexArray);