clang-format: [JS/TypeScript] Support "enum" as an optional property name, too.

Before:
  enum?: string
  [];

After:
  enum?: string[];

llvm-svn: 259628
diff --git a/clang/unittests/Format/FormatTestJS.cpp b/clang/unittests/Format/FormatTestJS.cpp
index 5807041..7f25d59 100644
--- a/clang/unittests/Format/FormatTestJS.cpp
+++ b/clang/unittests/Format/FormatTestJS.cpp
@@ -804,6 +804,7 @@
   verifyFormat("interface I {\n"
                "  x: string;\n"
                "  enum: string[];\n"
+               "  enum?: string[];\n"
                "}\n"
                "var y;");
   // Ensure that state is reset after parsing the interface.