chore: Update LLVM requirement

To build successfully with Xcode 11's toolchain we need
LLVM version 8.0.0

README.md

@@ -22,7 +22,7 @@ git clone --recursive git@github.com:NativeScript/ios-runtime.git
 - OS X 10.11+
 - [Xcode 10+](https://developer.apple.com/xcode/)
 - CMake 3.12 or later. Tested with versions up to 3.14.4 (https://github.com/Kitware/CMake/releases/download/v3.14.4/cmake-3.14.4-Darwin-x86_64.dmg) - after installing CMake.app add a symlink to cmake in `usr/local/bin` using the following command `ln -s /Applications/CMake.app/Contents/bin/cmake /usr/local/bin`
-- [llvm 7.0](http://releases.llvm.org/download.html#7.0.0) - 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/`.
+- [LLVM 8.0](http://releases.llvm.org/download.html#8.0.0) - 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`.
 - [Perl (installed on macOS by default but deprecated since macOS X 10.15)](https://www.perl.org/get.html#osx)