Backends: OpenGL: On OSX, if unspecified by app, made default GLSL version 150. (#3199)

docs/CHANGELOG.txt

@@ -55,6 +55,7 @@ Other Changes:
 - Backends: Win32: Fix _WIN32_WINNT < 0x0600 (MinGW defaults to 0x502 == Windows 2003). (#3183)
 - Backends: OpenGL: Fixed handling of GL 4.5+ glClipControl(GL_UPPER_LEFT) by inverting the
   projection matrix top and bottom values. (#3143, #3146) [@u3shit]
+- Backends: OpenGL: On OSX, if unspecified by app, made default GLSL version 150. (#3199) [@albertvaka]
 - Backends: Vulkan: Fixed error in if initial frame has no vertices. (#3177)
 - Backends: Vulkan: Fixed edge case where render callbacks wouldn't be called if the ImDrawData
   structure didn't have any vertices. (#2697) [@kudaba]

examples/imgui_impl_opengl3.cpp

@@ -13,6 +13,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2020-05-08: OpenGL: Made default GLSL version 150 (instead of 130) on OSX.
 //  2020-04-21: OpenGL: Fixed handling of glClipControl(GL_UPPER_LEFT) by inverting projection matrix.
 //  2020-04-12: OpenGL: Fixed context version check mistakenly testing for 4.0+ instead of 3.2+ to enable ImGuiBackendFlags_RendererHasVtxOffset.
 //  2020-03-24: OpenGL: Added support for glbinding 2.x OpenGL loader.
@@ -184,6 +185,9 @@ bool    ImGui_ImplOpenGL3_Init(const char* glsl_version)
 #elif defined(IMGUI_IMPL_OPENGL_ES3)
     if (glsl_version == NULL)
         glsl_version = "#version 300 es";
+#elif defined(__APPLE__)
+    if (glsl_version == NULL)
+        glsl_version = "#version 150";
 #else
     if (glsl_version == NULL)
         glsl_version = "#version 130";