```Typo fixes in the documentation

Contributed by @sarlinpe

Change-Id: I26435bbcb4b99886c7df76cfb798fcf13589db2d
```
```diff --git a/docs/source/nnls_covariance.rst b/docs/source/nnls_covariance.rst
index ece6f58..f95d246 100644
--- a/docs/source/nnls_covariance.rst
+++ b/docs/source/nnls_covariance.rst
```
```@@ -50,7 +50,7 @@
covariance of :math:`y`, then the maximum likelihood problem to be
solved is

-o.. math:: x^* = \arg \min_x f'(x) S^{-1} f(x)
+.. math:: x^* = \arg \min_x f'(x) S^{-1} f(x)

and the corresponding covariance estimate of :math:`x^*` is given by

```
```diff --git a/docs/source/nnls_modeling.rst b/docs/source/nnls_modeling.rst
index 8b84066..be87149 100644
--- a/docs/source/nnls_modeling.rst
+++ b/docs/source/nnls_modeling.rst
```
```@@ -1331,7 +1331,7 @@
element.
2. For all :math:`y` on the manifold, :math:`\boxplus(x,
\boxminus(y,x)) = y`. This ensures that any :math:`y` can be
-   reached from math:`x`.
+   reached from :math:`x`.
3. For all :math:`\Delta`, :math:`\boxminus(\boxplus(x, \Delta), x) =
\Delta`. This ensures that :math:`\boxplus` is an injective
(one-to-one) map.
```