Fix no-lone-template warning on Firmware page

Fixes https://eslint.vuejs.org/rules/no-lone-template.html

Signed-off-by: Yoshie Muranaka <yoshiemuranaka@gmail.com>
Change-Id: Icc92d8349f063d756b92f6b2f751f7804267effb
diff --git a/src/views/Configuration/Firmware/Firmware.vue b/src/views/Configuration/Firmware/Firmware.vue
index d4aef19..d9f337f 100644
--- a/src/views/Configuration/Firmware/Firmware.vue
+++ b/src/views/Configuration/Firmware/Firmware.vue
@@ -113,9 +113,7 @@
                 >
                   <template #invalid>
                     <b-form-invalid-feedback role="alert">
-                      <template>
-                        {{ $t('global.form.required') }}
-                      </template>
+                      {{ $t('global.form.required') }}
                     </b-form-invalid-feedback>
                   </template>
                 </form-file>