Fix spelling of single sign-on (#6621)

* Create signup_controller.jsx

* Create email_authentication_settings.jsx

* Create en.json

webapp/components/admin_console/email_authentication_settings.jsx

@@ -56,7 +56,7 @@ export default class EmailAuthenticationSettings extends AdminSettings {
                     helpText={
                         <FormattedMessage
                             id='admin.email.allowSignupDescription'
-                            defaultMessage='When true, Mattermost allows team creation and account signup using email and password.  This value should be false only when you want to limit signup to a single-sign-on service like OAuth or AD/LDAP.'
+                            defaultMessage='When true, Mattermost allows team creation and account signup using email and password.  This value should be false only when you want to limit signup to a single sign-on service like OAuth or AD/LDAP.'
                         />
                     }
                     value={this.state.enableSignUpWithEmail}

webapp/components/signup/signup_controller.jsx

@@ -169,7 +169,7 @@ export default class SignupController extends React.Component {
                         <span>
                             <FormattedMessage
                                 id='signup.gitlab'
-                                defaultMessage='GitLab Single-Sign-On'
+                                defaultMessage='GitLab Single Sign-On'
                             />
                         </span>
                     </span>

webapp/i18n/en.json

@@ -236,7 +236,7 @@
   "admin.email.agreeHPNS": " I understand and accept the Mattermost Hosted Push Notification Service <a href=\"https://about.mattermost.com/hpns-terms/\" target='_blank'>Terms of Service</a> and <a href=\"https://about.mattermost.com/hpns-privacy/\" target='_blank'>Privacy Policy</a>.",
   "admin.email.allowEmailSignInDescription": "When true, Mattermost allows users to sign in using their email and password.",
   "admin.email.allowEmailSignInTitle": "Enable sign-in with email: ",
-  "admin.email.allowSignupDescription": "When true, Mattermost allows team creation and account signup using email and password.  This value should be false only when you want to limit signup to a single-sign-on service like OAuth or AD/LDAP.",
+  "admin.email.allowSignupDescription": "When true, Mattermost allows team creation and account signup using email and password.  This value should be false only when you want to limit signup to a single sign-on service like OAuth or AD/LDAP.",
   "admin.email.allowSignupTitle": "Enable account creation with email: ",
   "admin.email.allowUsernameSignInDescription": "When true, Mattermost allows users to sign in using their username and password.  This setting is typically only used when email verification is disabled.",
   "admin.email.allowUsernameSignInTitle": "Enable sign-in with username: ",
@@ -1997,7 +1997,7 @@
   "sidebar_right_menu.teamSettings": "Team Settings",
   "sidebar_right_menu.viewMembers": "View Members",
   "signup.email": "Email and Password",
-  "signup.gitlab": "GitLab Single-Sign-On",
+  "signup.gitlab": "GitLab Single Sign-On",
   "signup.google": "Google Account",
   "signup.ldap": "AD/LDAP Credentials",
   "signup.office365": "Office 365",