Properly export CubeMapTextureArray symbols.

Only the maxSize() function was non-inline and apparently wasn't used
(or tested) until now, meh.

src/Magnum/CubeMapTextureArray.h

@@ -82,7 +82,7 @@ the six sides of the cube map, fourth part is layer in the array. See
 @requires_gl40 Extension @extension{ARB,texture_cube_map_array}
 @requires_gl Cube map texture arrays are not available in OpenGL ES.
 */
-class CubeMapTextureArray: public AbstractTexture {
+class MAGNUM_EXPORT CubeMapTextureArray: public AbstractTexture {
     public:
         /**
          * @brief Constructor