fix spanId format

[conord33]

I am not sure if this is the best place to change the spanId format. Another option would be to do it in the core/utils spanId generator, but I am not sure if other exporters or propagators expect the spanId to be in a certain format.

closes #161

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[conord33]

I signed it!

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CLAs look good, thanks!

[isaikevych]

Could you please add some test?

[conord33]

Yeah will do

[conord33]

Looks like this would also be fixed by upgrading to the V2 cloud trace api instead of using V1.

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CLAs look good, thanks!

[conord33]

@isaikevych I updated the tests. Let me know what you think when you get a chance.

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CLAs look good, thanks!

[isaikevych]

Thank you

[angelomichel]

Can we have a new release fixing the original issue (Invalid spanId error stackdriver-exporter, which seems to be resolved with this PR)?

We're running into the same issue.