Update update-checkout config to support swift-5.1-branch-06-12-2019

Author: shahmishal

utils/update_checkout/update-checkout-config.json

@@ -322,6 +322,32 @@
                 "sourcekit-lsp": "swift-5.1-branch"
             }
         },
+        "swift-5.1-branch-06-12-2019" : {
+            "aliases": ["swift-5.1-branch-06-12-2019"],
+            "repos": {
+                "llvm": "swift-5.1-branch",
+                "clang": "swift-5.1-branch",
+                "compiler-rt": "swift-5.1-branch",
+                "swift": "swift-5.1-branch-06-12-2019",
+                "lldb": "swift-5.1-branch",
+                "cmark": "master",
+                "llbuild": "swift-5.1-branch",
+                "swiftpm": "swift-5.1-branch",
+                "swift-syntax": "swift-5.1-branch",
+                "swift-stress-tester": "swift-5.1-branch",
+                "swift-corelibs-xctest": "swift-5.1-branch",
+                "swift-corelibs-foundation": "swift-5.1-branch",
+                "swift-corelibs-libdispatch": "swift-5.1-branch",
+                "swift-integration-tests": "swift-5.1-branch",
+                "swift-xcode-playground-support": "swift-5.1-branch",
+                "ninja": "release",
+                "icu": "release-61-1",
+                "clang-tools-extra": "swift-5.1-branch",
+                "libcxx": "swift-5.1-branch",
+                "indexstore-db": "swift-5.1-branch",
+                "sourcekit-lsp": "swift-5.1-branch"
+            }
+        },
         "stdlib_standalone" : {
             "aliases": ["stdlib_standalone"],
             "repos": {