Fixing documentation typo.

- Matrix had two columns squeezed together

Change-Id: I5f18df15364bd8507db98d43f8a547a9efab0913

docs/source/nnls_covariance.rst

diff --git a/docs/source/nnls_covariance.rst b/docs/source/nnls_covariance.rst
index 9c6cea8..d3b2273 100644
--- a/docs/source/nnls_covariance.rst
+++ b/docs/source/nnls_covariance.rst
@@ -207,7 +207,7 @@
 
      (J'J)^{-1} = \begin{bmatrix}
                   2.0471e+14&  -2.0471e+14 \\
-                  -2.0471e+14   2.0471e+14
+                  -2.0471e+14&   2.0471e+14
                   \end{bmatrix}