Update llvm version to 4.0.0 in README.md

Author: ivanbuhov

README.md

@@ -8,7 +8,7 @@ git clone --recursive [email protected]:NativeScript/ios-runtime.git
  - OS X 10.11+
  - [Xcode 8+](https://developer.apple.com/xcode/)
  - [CMake 3.1.3](https://cmake.org/files/v3.1/cmake-3.1.3-Darwin-x86_64.dmg) - Make sure to install the command line tools from the menu. Alternatively you can use [the cmake 3.1 installation script](https://gist.github.com/hdeshev/d96570189c332bb0bf67b3506dfd9760).
- - [llvm 3.9](http://www.llvm.org/releases/download.html#3.9.0) - used to build the [metadata generator](https://github.com/NativeScript/ios-metadata-generator) submodule. Be sure to have the folder containing `llvm-config` in `PATH` or make a symlink to in `/usr/local/bin/`.
+ - [llvm 4.0.0](http://www.llvm.org/releases/download.html#4.0.0) - used to build the [metadata generator](https://github.com/NativeScript/ios-metadata-generator) submodule. Be sure to have the folder containing `llvm-config` in `PATH` or make a symlink to in `/usr/local/bin/`.
  - [Automake](https://www.gnu.org/software/automake/) - available in [Homebrew](http://brew.sh) as `automake`.
  - [GNU Libtool](http://www.gnu.org/software/libtool/) - available in [Homebrew](http://brew.sh) as `libtool`.
  - Checkout all git submodules using `git submodule update --init`.