Update version 0.5.0 -> 0.5.1

Author: arcondello

dwave/preprocessing/__init__.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-__version__ = '0.5.0'
+__version__ = '0.5.1'
 
 from dwave.preprocessing import *
 import dwave.preprocessing.composites