Need a dependency

When I update to node 4.x I got the following error:

```
> canvas@1.4.0 install /app/web-server/node_modules/canvas
> node-gyp rebuild

make: Entering directory `/dist/web-server/node_modules/canvas/build'
SOLINK_MODULE(target) Release/obj.target/canvas-postbuild.node
COPY Release/canvas-postbuild.node
CXX(target) Release/obj.target/canvas/src/Canvas.o
In file included from ../src/Canvas.h:22:0,
from ../src/Canvas.cc:7:
../../nan/nan.h:43:3: error: #error This version of node/NAN/v8 requires a C++11 compiler
In file included from ../src/Canvas.h:11:0,
from ../src/Canvas.cc:7:

```

The solution was install C++ compiler.

We need to include this lines to the docker file and test:
https://gist.github.com/omnus/6404505