fix profile_vm.py script

Author: pipermerriam

ethereum/tests/profile_vm.py

@@ -3,10 +3,10 @@
 import ethereum.testutils as testutils
 import cProfile
 import pstats
-import StringIO
+from io import StringIO
 import time
 from rlp.utils import encode_hex
-from ethereum.utils import sha3
+from ethereum.utils import sha3, to_string
 from ethereum.slogging import get_logger
 logger = get_logger()
 
@@ -31,15 +31,15 @@ def run(profiler=None):
                 if i == num:
                     break
                 do_test_vm(filename, testname, testdata, profiler=profiler)
-                seen += str(testname)
+                seen += to_string(testname)
                 i += 1
         print('ran %d tests' % i)
         print('test key', encode_hex(sha3(seen)))
 
     if len(sys.argv) == 1:
         pr = cProfile.Profile()
         run(pr)
-        s = StringIO.StringIO()
+        s = StringIO()
         sortby = 'tottime'
         ps = pstats.Stats(pr, stream=s).sort_stats(sortby)
         ps.print_stats(50)