Update to python 3.

tests/test_transform_germline.py

@@ -3,7 +3,7 @@
 import pytest
 import os
 import pandas as pd
-from StringIO import StringIO
+from io import StringIO
 import transform_germline_mutations
 
 

tests/test_transform_imaging.py

@@ -3,7 +3,7 @@
 import pytest
 import os
 import pandas as pd
-from StringIO import StringIO
+from io import StringIO
 import transform_imaging
 
 

tests/test_transform_labs.py

@@ -3,7 +3,7 @@
 import pytest
 import os
 import pandas as pd
-from StringIO import StringIO
+from io import StringIO
 import transform_labs
 
 

tests/test_transform_patients.py

@@ -2,7 +2,7 @@
 
 import pytest
 import pandas as pd
-from StringIO import StringIO
+from io import StringIO
 import transform_patients
 
 

tests/test_transform_vitals.py

@@ -3,7 +3,7 @@
 import pytest
 import os
 import pandas as pd
-from StringIO import StringIO
+from io import StringIO
 import transform_vitals