[FSSDK-12546] bump version to 5.6.0

Author: jaeopt

optimizely/version.py

@@ -11,5 +11,5 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-version_info = (5, 5, 0)
+version_info = (5, 6, 0)
 __version__ = '.'.join(str(v) for v in version_info)