fix for writeProperty fail

[bing-mao]

Checklist

• I've read and followed the Contribution Guide.
• My commit messages reference affected issues and mention breaking changes if applicable.
• I've updated / wrote inline documentation for the source code affected by my changes.
• All mandatory CI checks have passed (see when Pull Request has been submitted).

Open Question

What does this Pull Request do

[DiniFarb]

I was facing the same issue as described in #138.

I digged in and found that in the writeProperty function, if no priority in the optional options object is set the value will be undefined and then not set in the protocol.
Speaking of this function:

node-bacstack/lib/client.js

Line 615 in 9e19310

writeProperty(address, objectId, propertyId, values, options, next) {

Here a test with priority in options set (left side) and without (right side).

So I was about to create a PR to fix it but luckely I came across this PR and saw that it already has 😄

Therefore just wanted to confirm that this PR solves #138 😉