Support node v6

[domosapien]

> [email protected] install .../node_modules/modern-syslog
> node-gyp rebuild

make: Entering directory `.../node_modules/modern-syslog/build'
  CXX(target) Release/obj.target/core/core.o
In file included from ../core.cc:2:0:
../../nan/nan.h:590:20: error: variable or field ‘AddGCEpilogueCallback’ declared void
       v8::Isolate::GCEpilogueCallback callback
                    ^
../../nan/nan.h:590:7: error: ‘GCEpilogueCallback’ is not a member of ‘v8::Isolate’
       v8::Isolate::GCEpilogueCallback callback
       ^
../../nan/nan.h:591:18: error: expected primary-expression before ‘gc_type_filter’
     , v8::GCType gc_type_filter = v8::kGCTypeAll) {
                  ^
../../nan/nan.h:596:20: error: variable or field ‘RemoveGCEpilogueCallback’ declared void
       v8::Isolate::GCEpilogueCallback callback) {
                    ^
../../nan/nan.h:596:7: error: ‘GCEpilogueCallback’ is not a member of ‘v8::Isolate’
       v8::Isolate::GCEpilogueCallback callback) {
       ^
../../nan/nan.h:601:20: error: variable or field ‘AddGCPrologueCallback’ declared void
       v8::Isolate::GCPrologueCallback callback
                    ^
../../nan/nan.h:601:7: error: ‘GCPrologueCallback’ is not a member of ‘v8::Isolate’
       v8::Isolate::GCPrologueCallback callback
       ^
../../nan/nan.h:602:18: error: expected primary-expression before ‘gc_type_filter’
     , v8::GCType gc_type_filter = v8::kGCTypeAll) {
                  ^
../../nan/nan.h:607:20: error: variable or field ‘RemoveGCPrologueCallback’ declared void
       v8::Isolate::GCPrologueCallback callback) {
                    ^
../../nan/nan.h:607:7: error: ‘GCPrologueCallback’ is not a member of ‘v8::Isolate’
       v8::Isolate::GCPrologueCallback callback) {
       ^
make: *** [Release/obj.target/core/core.o] Error 1
make: Leaving directory `.../node_modules/modern-syslog/build'

Updating nan to v2.3.5 will fix the issue.

[domosapien]

#13 submitted

[sam-github]

It does, user error, see #13.