fix(deps): update module github.com/mailgun/mailgun-go/v4 to v4.18.3

go.mod

@@ -19,7 +19,7 @@ require (
 	github.com/dghubble/oauth1 v0.7.3
 	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 v4.18.1
+	github.com/mailgun/mailgun-go/v4 v4.18.3
 	github.com/plivo/plivo-go/v7 v7.54.0
 	github.com/sendgrid/sendgrid-go v3.16.0+incompatible
 	github.com/silenceper/wechat/v2 v2.1.7

go.sum

@@ -257,8 +257,8 @@ github.com/line/line-bot-sdk-go v7.8.0+incompatible h1:Uf9/OxV0zCVfqyvwZPH8CrdiH
 github.com/line/line-bot-sdk-go v7.8.0+incompatible/go.mod h1:0RjLjJEAU/3GIcHkC3av6O4jInAbt25nnZVmOFUgDBg=
 github.com/mailgun/errors v0.4.0 h1:6LFBvod6VIW83CMIOT9sYNp28TCX0NejFPP4dSX++i8=
 github.com/mailgun/errors v0.4.0/go.mod h1:xGBaaKdEdQT0/FhwvoXv4oBaqqmVZz9P1XEnvD/onc0=
-github.com/mailgun/mailgun-go/v4 v4.18.1 h1:ShNH/wzj7albTF/6le011FF+DGMd3azcSKL4iO9AgeI=
-github.com/mailgun/mailgun-go/v4 v4.18.1/go.mod h1:+d4FCswFAukgYc1XtKK2IxOYaVxjVm8AN2z/5TBiT8M=
+github.com/mailgun/mailgun-go/v4 v4.18.3 h1:gP5Mbx7Qqhnz+903OATdLpH1wdLxpv5nn4BNOP2z9HU=
+github.com/mailgun/mailgun-go/v4 v4.18.3/go.mod h1:+d4FCswFAukgYc1XtKK2IxOYaVxjVm8AN2z/5TBiT8M=
 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=