Do not install Ninja on CI services

.circleci/install_dependencies.sh

@@ -12,16 +12,15 @@ set -e
 brew update || brew update
 
 # List of homebrew formulae to install in the order they appear.
-# We require CMake and Ninja for our build and tests, and all the others are
-# dependencies of pyenv.
+# We require CMake for our build and tests, and all the others are dependencies
+# of pyenv.
 REQUIREMENTS="cmake
-              ninja
               readline
               autoconf
               pkg-config
               openssl"
 
-# Install CMake, Ninja, and pyenv dependencies.
+# Install CMake and pyenv dependencies.
 for pkg in $REQUIREMENTS; do
   # Install package, or upgrade it if it is already installed.
   brew install $pkg || brew outdated $pkg || brew upgrade $pkg

.travis.yml

@@ -29,7 +29,6 @@ addons:
      # 4.8 is the first version of GCC with good enough C++11 support to build
      # ycmd.
      - g++-4.8
-     - ninja-build
      # Everything below is a Python build dep (though it depends on Python
      # version). We need them because pyenv builds Python.
      - libssl-dev