enable Python 2.7 on travis, fix two AttributeError issues (#10)

Author: xadupre

.appveyor.yml

@@ -19,7 +19,7 @@ install:
     - "%PYTHON%\\python -m pip install --upgrade pip"
     - "%PYTHON%\\Scripts\\pip install -r requirements.txt"
     - "%PYTHON%\\Scripts\\pip install git+https://github.com/apple/coremltools"
-    - "%PYTHON%\\Scripts\\pip install https://github.com/xadupre/xgboost/releases/download/0.7/xgboost-0.7-cp36-cp36m-win_amd64.whl"
+    - "if %PYTHON%==C:\\Python36-x64 %PYTHON%\\Scripts\\pip install https://github.com/xadupre/xgboost/releases/download/0.7/xgboost-0.7-cp36-cp36m-win_amd64.whl"
     - "%PYTHON%\\Scripts\\pip install -r requirements-dev.txt"
     - set PYTHONPATH=%~dp0
 
@@ -34,7 +34,6 @@ after_test:
     - if not exist dist\htmlcov mkdir dist\htmlcov
     - xcopy htmlcov dist\htmlcov
     - copy *.xml dist\htmlcov
-    - if %APPVEYOR_ACCOUNT_NAME%==xadupre %PYTHON%\Scripts\codecov -f coverage.xml -t 2c916354-0f91-46b4-a577-f80b0031c941
 
 artifacts:
     - path: dist

.travis.yml

@@ -1,6 +1,7 @@
 dist: trusty
 language: python
 python:
+    - "2.7"
     - "3.5"
     - "3.6"
 install: 

onnxmltools/convert/common/ConvertContext.py

@@ -59,4 +59,4 @@ def add_output(self, output):
         self._outputs.append(output)
 
     def clear_outputs(self):
-        self._outputs.clear()
+        del self._outputs[:]

tests/utils/test_utils.py

@@ -39,7 +39,11 @@ def test_save_text(self):
         json_file = os.path.join(this, "models", "coreml_OneHotEncoder_BikeSharing.json")
         json_file_new = os.path.join(this, "models", "coreml_OneHotEncoder_BikeSharing_new.json")
         save_text(onnx_model, json_file_new)
-        filecmp.clear_cache()
+        try:
+            filecmp.clear_cache()
+        except AttributeError:
+            # Only available in Python 3
+            pass
         content1 = self._parseEOL(json_file)
         content2 = self._parseEOL(json_file_new)
         self.assertTrue(content1 == content2,