Fix grammatical mistake

Fixed a grammatical mistake in arguments.md at line 20 in the second sentence. More specifically there was a duplicate 'is' word.

Author: Gregzeee

docssrc/src/arguments.md

@@ -17,7 +17,7 @@ List<Argument> arguments = new ArrayList<>();
 arguments.add(new PlayerArgument("target"));
 ```
 
-The String value is the node that is registered into Minecraft's internal command graph. This is name is also used as a prompt that is shown to a player when they are entering the command.
+The String value is the node that is registered into Minecraft's internal command graph. This name is also used as a prompt that is shown to a player when they are entering the command.
 
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