Modify Square_Root_by_Newton's_Method.scm

I've substitute the procedure name 'sqrt' with 'square-root'for
avoiding contradicting with the constant primitive in many Scheme
implementations. Now, this file should be able to be executed
normally by most Scheme interpreters.

Thank you!
						Lawrence R. Amlord
						   Mar. 31, 2013
						   Xi'an, China