Fix to gender-neutral singular pronoun (#1837)

app/js/locales/en-us.json

@@ -452,7 +452,7 @@
 	"error_modal_recovery_na_description": "Since you haven't provided a recovery e-mail when setting up your password, your remaining options are either to remember your password or to reset your account.",
 	"error_modal_password_success_descripion": "Your password for Two-Step Verification is now active.",
 	"error_modal_password_disabled_descripion": "You have disabled Two-Step Verification.",
-	"error_modal_user_not_mutual_contact": "The user can be invited by his contact only",
+	"error_modal_user_not_mutual_contact": "The user can be invited by their contact only",
 	"error_modal_invite_link_invalid": "The invite link is invalid",
 	"error_modal_channel_not_accessible": "Sorry, this channel is not accessible.",
 	"error_modal_not_contact_flood": "Sorry, you can only send messages to mutual contacts at the moment. {more-info-link: More info »}",