Applying reviewer feedback

Tidying style rules
Tidy tests
Added new test checking that installation won't render
Added snapshot test for code-instruction

ee/spec/frontend/packages/details/components/installation_spec.js

@@ -34,6 +34,10 @@ describe('PackageInstallation', () => {
     });
   }
 
+  beforeEach(() => {
+    createComponent();
+  });
+
   afterEach(() => {
     if (wrapper) wrapper.destroy();
   });