Fixed component swapping in tmat2x2::_inverse().

NB: glm::detail::tmat2x2::_inverse() incorrectly swaps all components instead of only main diagonals:

	A = ⌈a  b⌉
	    ⌊c  d⌋

(using standard representation). _inverse() on A incorrectly gives the order

	⌈ d  -c⌉
	⌊-b   a⌋

(swaps both diagonals) where it should be

	⌈ d  -b⌉
	⌊-c   a⌋

(I am leaving out division by the determinate for clarity).

Also, glm::inverse() in `glm/core/func_matrix.inl` is correct for 2x2 matrices and shows the mistake of _inverse().
The unit tests do not appear to test division of a mat2 by a mat2 (where this could arise).

glm/core/type_mat2x2.inl

@@ -271,8 +271,8 @@ namespace detail
 
         tmat2x2<T> Inverse(
             + this->value[1][1] / Determinant,
+            - this->value[0][1] / Determinant,
             - this->value[1][0] / Determinant,
-            - this->value[0][1] / Determinant, 
             + this->value[0][0] / Determinant);
         return Inverse;
     }