Fix UnicodeDecocdError when profile result writing to filestream

[amyangfei]

From the following code tmp is a str type object in python2, which can be wrote to file directly. Otherwise calling unicode on it will cause UnicodeDecodeError.

memory_profiler/memory_profiler.py

Lines 779 to 780 in 5106293

	tmp = template.format(lineno, mem, inc, all_lines[lineno - 1])
	stream.write(unicode(tmp, 'UTF-8'))

[fabianp]

thanks!