Fix naming of variable

Author: tohyuting

src/main/java/seedu/clinic/logic/commands/HelpCommand.java

@@ -19,7 +19,7 @@ public class HelpCommand extends Command {
             + "following keywords: add, clear, delete, exit, find, view, update";
 
     public static final String SHOWING_HELP_MESSAGE = "Opened help window.";
-    public static final String[] ALLOWED_ARGUMENT = new String[]{
+    public static final String[] ALLOWED_ARGUMENTS = new String[]{
         "add", "clear", "delete", "exit", "find", "list", "view", "update"};
 
     public static final String HELP_MESSAGE_FOR_COMMAND_FORMAT = "How to interpret command format?\n"

src/main/java/seedu/clinic/logic/parser/HelpCommandParser.java

@@ -1,7 +1,7 @@
 package seedu.clinic.logic.parser;
 
 import static seedu.clinic.commons.core.Messages.MESSAGE_INVALID_COMMAND_FORMAT;
-import static seedu.clinic.logic.commands.HelpCommand.ALLOWED_ARGUMENT;
+import static seedu.clinic.logic.commands.HelpCommand.ALLOWED_ARGUMENTS;
 import static seedu.clinic.logic.commands.HelpCommand.MESSAGE_TOO_MANY_ARGUMENTS;
 import static seedu.clinic.logic.commands.HelpCommand.MESSAGE_WRONG_ARGUMENT;
 
@@ -31,7 +31,7 @@ public HelpCommand parse(String args) throws ParseException {
                     MESSAGE_TOO_MANY_ARGUMENTS));
         }
         String helpArgument = helpKeyword[0].toLowerCase();
-        if (!Arrays.asList(ALLOWED_ARGUMENT).contains(helpArgument)) {
+        if (!Arrays.asList(ALLOWED_ARGUMENTS).contains(helpArgument)) {
             throw new ParseException(String.format(MESSAGE_INVALID_COMMAND_FORMAT,
                     MESSAGE_WRONG_ARGUMENT));
         }