Added test case for CCITTFaxDecoder (#700)

* array.array.tostring -> array.array.tobytes

The tostring method has been deprecated since Python 3.2 and was
removed altogether in 3.9. In Python 3.2 the method was renamed
to "tobytes"

Will close #641

* changelog entry

* test for tobytes

* Fix CHANGELOG.md

* Update CHANGELOG.md to PR that I can push on

* Simplify tests

Co-authored-by: Forest Gregg <fgregg@uchicago.edu>

tests/test_pdfminer_ccitt.py

@@ -1,6 +1,6 @@
 from nose.tools import assert_equal
 
-from pdfminer.ccitt import CCITTG4Parser
+from pdfminer.ccitt import CCITTG4Parser, CCITTFaxDecoder
 
 
 class TestCCITTG4Parser():
@@ -153,3 +153,11 @@ class TestCCITTG4Parser():
         parser._do_vertical(1)
         assert_equal(parser._get_bits(), '00000001')
         return
+
+
+class TestCCITTFaxDecoder:
+    def test_b1(self):
+        decoder = CCITTFaxDecoder(5)
+        decoder.output_line(0, b'0')
+        assert_equal(decoder.close(), b'\x80')
+        return