fixed CANCEL observe issue clientServlet.java

fixed CANCEL observe issue..
It is a bug in client servlet line 285 -> added forward slash before observe
before:
String target = StringUtils.substringsBetween(req.getPathInfo(), clientEndpoint, "observe")[0];
after:
String target = StringUtils.substringsBetween(req.getPathInfo(), clientEndpoint, "/observe")[0];

TARGET always = /objectId/objectInstance/resourceId/  ----- in ObservationRegistryImpl.java line 118, the key in the map does't contain the forward slash at the end..

I changed doPost also line 205 clientServlet.java.
I don't understand , how did I mess the import. Only changes I did is adding the forward slash before observe. 
That three lines  of import are needed and there were originally there. 

-import java.util.Collection;
-import java.util.HashMap;
-import java.util.Map;

Yes we can add Gemalto Inc Copyright, as we are interested in participating in leshan project.
Pls, let me know if you want me to change something else and pull another request?
Thanks,