Revert "Rename osx/high-sierra to osx-high-sierra"

This reverts commit bab45e8.

Author: Stefania Alborghetti

build.yaml

@@ -2,13 +2,13 @@ schedules:
   adhoc:
     schedule: adhoc
 os:
-  - osx-high-sierra
+  - osx/high-sierra
   - ubuntu/trusty64
 java:
   - oraclejdk8
 build:
   - script: |
-      if [ "$OS_VERSION" = "osx-high-sierra" ]; then
+      if [ "$OS_VERSION" = "osx/high-sierra" ]; then
          mvn -B clean package -DskipTests
          mvn -B -pl transport-native-unix-common,transport-native-kqueue -Partifactory deploy -DskipTests -DaltDeploymentRepository="artifactory::default::https://repo.datastax.com/datastax-releases-local"
       else