add fetch for tags

Author: edwardvalentini

.travis.yml

@@ -38,6 +38,7 @@ matrix:
     - export PATH=${PWD}/swift-4.1-RELEASE-ubuntu14.04/usr/bin:"${PATH}"
     - sudo ./swift-4.1-RELEASE-ubuntu14.04/usr/bin/swift utils/make-pkgconfig.swift
     script:
+    - git fetch --tags
     - git checkout tags/0.2.3
     - swift test
 #notifications: