command.java: Remove unnecessary `;` at the end of function

[tshradheya]

There is an unnecessary ; at the end of execute() function in Line 44

Noticed this while reviewing PR's for CS2103

addressbook-level2/src/seedu/addressbook/commands/Command.java

Lines 42 to 44 in 23644b1

	public CommandResult execute(){
	throw new UnsupportedOperationException("This method is to be implemented by child classes");
	};