Fix error in test_concat

Author: shoyer

.travis.yml

@@ -22,4 +22,4 @@ install:
   - python setup.py install
 # Run test
 script:
-  - nosetests -v
+  - nosetests

test/test_dataset.py

@@ -370,7 +370,7 @@ def test_concat(self):
             data0, data1 = deepcopy(split_data)
             data1['foo'] = ('bar', np.random.randn(10))
             Dataset.concat([data0, data1], 'dim1')
-        with self.assertRaisesRegexp(ValueError, 'not equal across datasets'):
+        with self.assertRaisesRegexp(ValueError, 'unsafe to merge datasets'):
             data0, data1 = deepcopy(split_data)
             data1['dim2'] *= 2
             Dataset.concat([data0, data1], 'dim1')