fix: unifies strings format

src/app/strings.ts

@@ -17,7 +17,7 @@ export const strings = Object.freeze({
     editTheContact: 'edit the contact',
     errorMessageMaxLength: (maxLen: number) => `must be ${maxLen} characters or fewer`,
     errorMessagePhonePattern: `valid format: + (optional) plus 12 to 15 digits`,
-    errorMessageRequired: 'this field is required.',
+    errorMessageRequired: 'this field is required',
     errorNotification: 'oops, there was an error',
     goBack: 'go back',
     name: 'name',
@@ -43,7 +43,7 @@ export const strings = Object.freeze({
     editTheContact: 'edite el contacto. ',
     errorMessageMaxLength: (maxLen: number) => `debe contener ${maxLen} caracteres or menos`,
     errorMessagePhonePattern: `formato: + (opcional) y 12 a 15 digitos`,
-    errorMessageRequired: 'este campo es requerido.',
+    errorMessageRequired: 'este campo es requerido',
     errorNotification: 'hubo un error',
     goBack: 'volver',
     name: 'nombre',