[fidl] Add newline after empty file error message.

Test: Ran formatter, verified output.
Change-Id: Ifaa8a0b12825153cadea19c6f11068afa09bf2b4
diff --git a/system/host/fidl/formatter/main.cpp b/system/host/fidl/formatter/main.cpp
index 3d85bdc..94dd2ee 100644
--- a/system/host/fidl/formatter/main.cpp
+++ b/system/host/fidl/formatter/main.cpp
@@ -91,7 +91,7 @@
 
     if (pos >= args.size()) {
         // TODO: Should probably read a file from stdin, instead.
-        FailWithUsage(args[0], "No files provided");
+        FailWithUsage(args[0], "No files provided\n");
     }
 
     fidl::SourceManager source_manager;