emit-modules-protobuf for long -e option

Co-authored-by: Jack Koenig <koenig@sifive.com>

src/main/scala/firrtl/Emitter.scala

@@ -153,7 +153,7 @@ object EmitAllModulesAnnotation extends HasShellOptions {
       helpValueName = Some("<chirrtl|high|middle|low|verilog|mverilog|sverilog>")
     ),
     new ShellOption[String](
-      longOption = "emit-module-protobufs",
+      longOption = "emit-modules-protobuf",
       toAnnotationSeq = (a: String) =>
         a match {
           case "chirrtl" =>