add version and required extension

let a chance to work on intel chipset

examples/osgdrawinstanced/osgdrawinstanced.cpp

@@ -59,6 +59,8 @@ createStateSet()
     // render each instance uniquely. gl_InstanceID will be in the range
     // 0 to numInstances-1 (1023 in our case).
     std::string vertexSource =
+        "#version 120\n"
+        "#extension GL_ARB_draw_instanced : enable\n"
         "uniform sampler2D osgLogo; \n"
         "uniform float osg_SimulationTime; \n"