updated to edgems-math

Update go.mod

Merge pull request #9 from MZDevinc/access-token-fix

aud field for access token

Merge pull request #8 from MZDevinc/custom-variable-fix

fixed launch message struct to be able to parse custom variables

Merge pull request #5 from MZDevinc/access-token-kid

add KID to access token request JWT

More descriptive error when access token fetch fails

Avoid nil pointer reference 2

Also, allow number as ToolPlatform guid

Avoid nil pointer reference

Client ID => AUD

Retrieve aud from aud if there's no client_id field

Merge branch 'master' of https://github.com/MZDevinc/go-lti