fix(account username): update regex validator

hiboo/account/forms.py

@@ -19,8 +19,8 @@ class TotpForm(flask_wtf.FlaskForm):
 class SignupForm(flask_wtf.FlaskForm):
     username = fields.StringField(_('Username'), [
         validators.DataRequired(),
-        validators.Regexp("[a-z0-9-_]", message="Your username must be \
-           comprised of lowercase letters and numbers only")
+        validators.Regexp("(^[a-z0-9-_]+$)", message=(_("Your username must be \
+           comprised of lowercase letters, numbers and '-' '_' only")))
     ])
     password = fields.PasswordField(_('Password'), [validators.DataRequired()])
     password2 = fields.PasswordField(_('Confirm password'),