[no not merge] upgrade to node v10

[mollymerp]

No description provided.

[mollymerp]

I wasn't aware that node 10 results in native crashes mapbox/mapbox-gl-native#12252 and also crashed the gl-js render tests on CI with

```node[97]: ../src/node_zlib.cc:176:static void node::{anonymous}::ZCtx::Write(const v8::FunctionCallbackInfo<v8::Value>&) [with bool async = false]: Assertion `Buffer::HasInstance(args[4])' failed.
 1: 0x8daaa0 node::Abort() [node]
 2: 0x8dab75  [node]
 3: 0x98fb5a  [node]
 4: 0xb5faef  [node]
 5: 0xb60659 v8::internal::Builtin_HandleApiCall(int, v8::internal::Object**, v8::internal::Isolate*) [node]
 6: 0x136df655be1d``` 

so we should hold on this til we can dig in further.

[mourner]

@mollymerp based on some googling of that render tests error, it seems that it could be fixed by upgrading pngjs to the latest version. But let's definitely still hold on updating the image before the native issue is resolved.

[kkaefer]

Superseded by #31; We now use node v10 by default, but currently only run tests on v8 because v10 is crashing as you noted.