Update to 1.8.0.

Change-Id: Id42e594f03e3575d06e18c1ef66df64f43d86839
diff --git a/docs/source/building.rst b/docs/source/building.rst
index f493c84..40d1f93 100644
--- a/docs/source/building.rst
+++ b/docs/source/building.rst
@@ -111,10 +111,10 @@
 
 .. code-block:: bash
 
- tar zxf ceres-solver-1.7.0.tar.gz
+ tar zxf ceres-solver-1.8.0.tar.gz
  mkdir ceres-bin
  cd ceres-bin
- cmake ../ceres-solver-1.7.0
+ cmake ../ceres-solver-1.8.0
  make -j3
  make test
 
@@ -124,7 +124,7 @@
 
 .. code-block:: bash
 
- bin/simple_bundle_adjuster ../ceres-solver-1.7.0/data/problem-16-22106-pre.txt
+ bin/simple_bundle_adjuster ../ceres-solver-1.8.0/data/problem-16-22106-pre.txt
 
 This runs Ceres for a maximum of 10 iterations using the
 ``DENSE_SCHUR`` linear solver. The output should look something like
@@ -214,10 +214,10 @@
 
 .. code-block:: bash
 
-   tar zxf ceres-solver-1.7.0.tar.gz
+   tar zxf ceres-solver-1.8.0.tar.gz
    mkdir ceres-bin
    cd ceres-bin
-   cmake ../ceres-solver-1.7.0
+   cmake ../ceres-solver-1.8.0
    make -j3
    make test