include additional dependency for clang format (#1181)

doc/sphinx/source/install.rst

@@ -20,7 +20,7 @@ with the following packages and prerequisites:
    :escape: ~
 
    CentOS 7.4 64-bit, GCC 4.8, CMake 3.4.3, supported, ``wget zlib-devel ncurses-libs ncurses-devel patch diffutils gcc-c++ make git perl-Data-Dumper`` 
-   Ubuntu 16.04 (LTS) 64-bit, Clang 3.9, CMake 3.5.1 + GNU Make, supported, ``build-essential cmake clang-3.9 git curl zlib1g zlib1g-dev libtinfo-dev``
+   Ubuntu 16.04 (LTS) 64-bit, Clang 3.9, CMake 3.5.1 + GNU Make, supported, ``build-essential cmake clang-3.9 clang-format-3.9 git curl zlib1g zlib1g-dev libtinfo-dev``
    Clear Linux\* OS for Intel Architecture, Clang 5.0.1, CMake 3.10.2, experimental, bundles ``machine-learning-basic dev-utils python3-basic python-basic-dev``
 
 Other configurations may work, but should be considered experimental with