[Update-checkout] Update the swift-4.2-branch to match clang, llvm, and compiler-rt branches

Author: shahmishal

utils/update-checkout-config.json

@@ -191,14 +191,14 @@
         "swift-4.2-branch" : {
             "aliases": ["swift-4.2-branch"],
             "repos": {
-                "llvm": "swift-4.1-branch",
-                "clang": "swift-4.1-branch",
+                "llvm": "swift-4.2-branch",
+                "clang": "swift-4.2-branch",
                 "swift": "swift-4.2-branch",
                 "lldb": "swift-4.2-branch",
                 "cmark": "master",
                 "llbuild": "master",
                 "swiftpm": "master",
-                "compiler-rt": "swift-4.1-branch",
+                "compiler-rt": "swift-4.2-branch",
                 "swift-corelibs-xctest": "master",
                 "swift-corelibs-foundation": "master",
                 "swift-corelibs-libdispatch": "master",