Fix failing Heroku review app

[kr8n3r]

In #827 we removed pinning the node version, instead specifying the minimum version.

This resulted in Heroku failing as there is an error in the gulp taks in node 10.5.0 Heroku installs.

Until we decide to upgrade to Gulp 4 we need to pin the version in package.json.

Alternative option is to remove version entirely, although we want to set that for anyone wanting to contribute using yarn instead of npm.

Heroku used Node 10.5, built and deployed correctly

Installing binaries
engines.node (package.json):  >= 8.9.4
engines.npm (package.json):   unspecified (use default)
       
Resolving node version >= 8.9.4...
Downloading and installing node 10.5.0...
Using default npm version: 6.1.0

Caching build
       Clearing previous node cache
       Skipping cache save (disabled by config)
-----> Pruning devDependencies
       Skipping because NPM_CONFIG_PRODUCTION is 'false'
-----> Build succeeded!
-----> Discovering process types
       Procfile declares types -> web
-----> Compressing...
       Done: 144.1M
-----> Launching...
       Released v517
       https://govuk-frontend-review.herokuapp.com/ deployed to Heroku

When requesting the site it threw a 503 error

2018-06-25T15:15:57.649864+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/favicon.ico" host=govuk-frontend-review.herokuapp.com request_id=180da83d-7c96-4c99-9a4e-52830e670538 fwd="195.89.171.5" dyno= connect= service= status=503 bytes= protocol=http

Firstly we tried removing the space between number and greaterOrEqual sign, but that didn't work.

[NickColley]

Can you add context to this commit that explains why we are pinning it again please?

[NickColley]

Needs commit that explains why we need to pin

And changelog entry until we make a decision on #834

[kr8n3r]

Update 10.5.0 fails with this

gulp[88868]: ../src/node_contextify.cc:629:static void node::contextify::ContextifyScript::New(const FunctionCallbackInfo<v8::Value> &): Assertion `args[1]->IsString()' failed.
 1: 0x100033c31 node::Abort() [/usr/local/bin/node]
 2: 0x100032c77 node::MakeCallback(v8::Isolate*, v8::Local<v8::Object>, char const*, int, v8::Local<v8::Value>*, node::async_context) [/usr/local/bin/node]
 3: 0x100058a4b node::contextify::ContextifyScript::New(v8::FunctionCallbackInfo<v8::Value> const&) [/usr/local/bin/node]
 4: 0x10022822f v8::internal::FunctionCallbackArguments::Call(v8::internal::CallHandlerInfo*) [/usr/local/bin/node]
 5: 0x1002273c8 v8::internal::MaybeHandle<v8::internal::Object> v8::internal::(anonymous namespace)::HandleApiCallHelper<true>(v8::internal::Isolate*, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::FunctionTemplateInfo>, v8::internal::Handle<v8::internal::Object>, v8::internal::BuiltinArguments) [/usr/local/bin/node]
 6: 0x100226d97 v8::internal::Builtin_Impl_HandleApiCall(v8::internal::BuiltinArguments, v8::internal::Isolate*) [/usr/local/bin/node]
 7: 0x3eb7788041bd
sh: line 1: 88868 Abort trap: 6           gulp copy-assets

and i found this cloudfour/core-gulp-tasks#63

Update to Gulp 4 in firebreak?

[kr8n3r]

updated with requested changes

[NickColley]

Great work, thanks Jani