GLES3: Fixed issue #259.

src/renderer_gl.cpp

@@ -5958,9 +5958,10 @@ namespace bgfx { namespace gl
 				{
 					if (BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGLES >= 30) )
 					{
-						writeString(&writer
+						writeStringf(&writer
 							, "#version 300 es\n"
-							  "precision mediump float;\n"
+							  "precision %s float;\n"
+							, m_type == GL_FRAGMENT_SHADER ? "mediump" : "highp"
 							);
 					}
 					else