Fix typo in AutoDiffManifold comment and docs

Change-Id: I0b50e3e10661578e68f713e34a59f65b3692e745

Author: MaximSmolskiy

docs/source/nnls_modeling.rst

@@ -1715,7 +1715,7 @@ templated ``Plus`` and ``Minus`` functions that compute:
   x_plus_delta = Plus(x, delta);
   y_minus_x    = Minus(y, x);
 
-Where, ``x``, ``y`` and ``x_plus_y`` are vectors on the manifold in
+Where, ``x``, ``y`` and ``x_plus_delta`` are vectors on the manifold in
 the ambient space (so they are ``kAmbientSize`` vectors) and
 ``delta``, ``y_minus_x`` are vectors in the tangent space (so they are
 ``kTangentSize`` vectors).

include/ceres/autodiff_manifold.h

@@ -47,8 +47,8 @@ namespace ceres {
 //   x_plus_delta = Plus(x, delta);
 //   y_minus_x    = Minus(y, x);
 //
-// Where, x, y and x_plus_y are vectors on the manifold in the ambient space (so
-// they are kAmbientSize vectors) and delta, y_minus_x are vectors in the
+// Where, x, y and x_plus_delta are vectors on the manifold in the ambient space
+// (so they are kAmbientSize vectors) and delta, y_minus_x are vectors in the
 // tangent space (so they are kTangentSize vectors).
 //
 // The Functor should have the signature: