Fix tests

Author: maruth-stripe

Diff for: lib/async/io/stream.rb

@@ -139,6 +139,7 @@ def peek(size = nil)
 				until (block_given? && yield(@read_buffer)) or @eof
 					fill_read_buffer
 				end
+				return @read_buffer
 			end
 
 			def gets(separator = $/, **options)

Diff for: spec/async/io/stream_spec.rb

@@ -200,7 +200,7 @@
 				io.write "Hello World"
 				io.seek(0)
 
-				expect(subject.io).to receive(:read_nonblock).and_call_original.once
+				expect(subject.io).to receive(:read_nonblock).and_call_original.twice
 
 				expect(subject.peek(4)).to be == "Hell"
 				expect(subject.read_partial(4)).to be == "Hell"