Updating dependencies to fix CI build leveldown error

[jmatsushita]

No description provided.

[jmatsushita]

Urgh this build error seems like a hard one... Any thoughts @mcollina ? Will try downgrading deps

In file included from /home/travis/.node-gyp/0.10.48/include/node/node.h:62:0,
                 from ../src/iterator.cc:6:
/home/travis/.node-gyp/0.10.48/include/node/v8.h: In static member function ‘static v8::Local<T> v8::Local<T>::Cast(v8::Local<S>) [with S = v8::Value, T = v8::Value]’:
/home/travis/.node-gyp/0.10.48/include/node/v8.h:292:32:   instantiated from ‘v8::Local<S> v8::Local<T>::As() [with S = v8::Value, T = v8::Value]’
../src/iterator.cc:273:61:   instantiated from here
/home/travis/.node-gyp/0.10.48/include/node/v8.h:288:35: error: ‘Cast’ is not a member of ‘v8::Value’
/home/travis/.node-gyp/0.10.48/include/node/v8.h:289:3: warning: control reaches end of non-void function [-Wreturn-type]
make: *** [Release/obj.target/leveldown/src/iterator.o] Error 1

[jmatsushita]

Ok got it. leveldown@1.5.3 seems to be the culprit.

[jmatsushita]

I'll close this and submit a squashed PR.