[LLDB] [NFC] Typo fix in usage text for "type filter" command

[xgupta]

Summary

When you invoke "help type filter" the resulting help shows:

Syntax: type synthetic [<sub-command-options>]

This patch fixes the help so it says "type filter" instead of "type synthetic".

patch by: "Daniel Jalkut <[e-mail]>"

lldb/source/Commands/CommandObjectType.cpp

   CommandObjectTypeFilter(CommandInterpreter &interpreter)
       : CommandObjectMultiword(interpreter, "type filter",
                                "Commands for operating on type filters.",
-                               "type synthetic [<sub-command-options>] ") {
+                               "type filter [<sub-command-options>] ") {
     LoadSubCommand(
         "add", CommandObjectSP(new CommandObjectTypeFilterAdd(interpreter)));
     LoadSubCommand("clear", CommandObjectSP(