GL: fix the value of Renderer::Memory::Barrier::ShaderStorage.

Sigh.

doc/changelog.dox

@@ -239,6 +239,7 @@ See also:
 
 -   @ref GL::Context move constructor was not marked @cpp noexcept @ce by
     accident
+-   @ref GL::Renderer::MemoryBarrier::ShaderStorage had an incorrect value
 -   @ref Platform::EmscriptenApplication randomly created antialiased contexts
     due to an uninitialized variable in its
     @ref Platform::EmscriptenApplication::GLConfiguration "GLConfiguration"

src/Magnum/GL/Renderer.h

@@ -1898,7 +1898,7 @@ class MAGNUM_GL_EXPORT Renderer {
              *      3.0 and older.
              * @requires_gles Shader storage is not available in WebGL.
              */
-            ShaderStorage = GL_ATOMIC_COUNTER_BARRIER_BIT
+            ShaderStorage = GL_SHADER_STORAGE_BARRIER_BIT
         };
 
         /**