Install dependencies for docs.

.travis.yml

@@ -86,7 +86,7 @@ cache:
         - jsoncpp
 
 install:
-    - test $JOB != default || ./scripts/install_deps.sh
+    - test $JOB != default -a $JOB != docs || ./scripts/install_deps.sh
 before_script:
     - test $JOB != emscripten || ./scripts/build_emscripten.sh
     - test $JOB != default || (mkdir -p build

scripts/install_deps.sh

@@ -202,6 +202,7 @@ case $(uname -s) in
                 # Install "normal packages"
                 sudo apt-get -y update
                 sudo apt-get -y install \
+                    python-sphinx \
                     build-essential \
                     cmake \
                     g++ \
@@ -306,6 +307,7 @@ case $(uname -s) in
 
                 sudo apt-get -y update
                 sudo apt-get -y install \
+                    python-sphinx \
                     build-essential \
                     cmake \
                     git \