Upgrade to jclouds 1.8.1

This release addresses multiple s3-tests failures:

s3tests.functional.test_s3.test_object_write_to_nonexist_bucket
s3tests.functional.test_s3.test_object_delete_key_bucket_gone

References #5.

pom.xml

@@ -169,7 +169,7 @@
 
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-    <jclouds.version>1.8.0</jclouds.version>
+    <jclouds.version>1.8.1</jclouds.version>
     <slf4j.version>1.7.7</slf4j.version>
   </properties>