Update README to provide status for Ubuntu 18.04 jobs

Author: shahmishal

README.md

@@ -9,6 +9,7 @@
 | **Ubuntu 14.04** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-14_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-14_04)|[![Build Status](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-14_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-14_04)|
 | **Ubuntu 16.04** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-16_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-16_04)|[![Build Status](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-16_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-16_04)|
 | **Ubuntu 16.10** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-16_10/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-16_10)|[![Build Status](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-16_10/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-16_10)|
+| **Ubuntu 18.04** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-18_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-18_04)|[![Build Status](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-18_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-18_04)|
 
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