Use GL_R8 instead of GL_RED on ES3

src/nanovg_gl3.h

@@ -453,7 +453,11 @@ static int glnvg__renderCreateTexture(void* uptr, int type, int w, int h, const
 	if (type == NVG_TEXTURE_RGBA)
 		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
 	else
+#ifdef NANOVG_GLES3
+		glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, w, h, 0, GL_RED, GL_UNSIGNED_BYTE, data);
+#else
 		glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, w, h, 0, GL_RED, GL_UNSIGNED_BYTE, data);
+#endif
 
 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);