Merge pull request swiftlang#66 from ArtSabintsev/master

Updated Guitar for Swift 4.0

Author: lplarson

projects.json

@@ -552,6 +552,9 @@
     "path": "Guitar",
     "branch": "master",
     "compatibility": {
+      "4.0": {
+        "commit": "d88afd48e8793d66f4609db98710b679ce039341"
+      },
       "3.1": {
         "commit": "f3135a5c1fc7ac079cf4156992455b254b16bb84"
       }