Add Apache snapshots repository

Needed by jclouds 2.0.0-SNAPSHOT.  Regression from
23f8e772da.  Fixes #37.

pom.xml

@@ -257,6 +257,16 @@
     <maven>3.0.5</maven>
   </prerequisites>
 
+  <repositories>
+    <repository>
+      <id>apache-snapshots</id>
+      <url>https://repository.apache.org/content/repositories/snapshots</url>
+      <snapshots>
+        <enabled>true</enabled>
+      </snapshots>
+    </repository>
+  </repositories>
+
   <dependencies>
     <dependency>
       <groupId>ch.qos.logback</groupId>