use BytesIO to work with python3

pyaccuwage/__init__.py

@@ -37,7 +37,7 @@ def test_dump():
         record.EmployerRecord(),
         record.EmployeeWageRecord(),
         ]
-    out = io.StringIO()
+    out = io.BytesIO()
     dump(records, out)
     return out
 
@@ -75,7 +75,7 @@ def load(fp):
 
 def loads(s):
     import io
-    fp = io.StringIO(s)
+    fp = io.BytesIO(s)
     return load(fp)
 
 
@@ -85,7 +85,7 @@ def dump(records, fp):
 
 def dumps(records):
     import io
-    fp = io.StringIO()
+    fp = io.BytesIO()
     dump(records, fp)
     fp.seek(0)
     return fp.read()