fix(deps): update module github.com/mailgun/mailgun-go/v4 to v4.12.0 (#766)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

go.mod

@@ -17,7 +17,7 @@ require (
 	github.com/dghubble/oauth1 v0.7.2
 	github.com/go-telegram-bot-api/telegram-bot-api v4.6.4+incompatible
 	github.com/line/line-bot-sdk-go v7.8.0+incompatible
-	github.com/mailgun/mailgun-go/v4 v4.11.1
+	github.com/mailgun/mailgun-go/v4 v4.12.0
 	github.com/pkg/errors v0.9.1
 	github.com/plivo/plivo-go/v7 v7.42.0
 	github.com/sendgrid/sendgrid-go v3.13.0+incompatible

go.sum

@@ -204,8 +204,8 @@ github.com/leodido/go-urn v1.2.4 h1:XlAE/cm/ms7TE/VMVoduSpNBoyc2dOxHs5MZSwAN63Q=
 github.com/leodido/go-urn v1.2.4/go.mod h1:7ZrI8mTSeBSHl/UaRyKQW1qZeMgak41ANeCNaVckg+4=
 github.com/line/line-bot-sdk-go v7.8.0+incompatible h1:Uf9/OxV0zCVfqyvwZPH8CrdiHXXmMRa/L91G3btQblQ=
 github.com/line/line-bot-sdk-go v7.8.0+incompatible/go.mod h1:0RjLjJEAU/3GIcHkC3av6O4jInAbt25nnZVmOFUgDBg=
-github.com/mailgun/mailgun-go/v4 v4.11.1 h1:d9wWlSTM11XrcN3hY1tJAXHv17IoVVf0TE5eZmSVEvU=
-github.com/mailgun/mailgun-go/v4 v4.11.1/go.mod h1:L9s941Lgk7iB3TgywTPz074pK2Ekkg4kgbnAaAyJ2z8=
+github.com/mailgun/mailgun-go/v4 v4.12.0 h1:TtuQCgqSp4cB6swPxP5VF/u4JeeBIAjTdpuQ+4Usd/w=
+github.com/mailgun/mailgun-go/v4 v4.12.0/go.mod h1:L9s941Lgk7iB3TgywTPz074pK2Ekkg4kgbnAaAyJ2z8=
 github.com/mattn/go-colorable v0.1.13 h1:fFA4WZxdEF4tXPZVKMLwD8oUnCTTo08duU7wxecdEvA=
 github.com/mattn/go-colorable v0.1.13/go.mod h1:7S9/ev0klgBDR4GtXTXX8a3vIGJpMovkB8vQcUbaXHg=
 github.com/mattn/go-isatty v0.0.16/go.mod h1:kYGgaQfpe5nmfYZH+SKPsOc2e4SrIfOl2e/yFXSvRLM=