feat(CLI): Exit with 1 when diff is not empty.

To make it easier to use the diff command in scripts and CI and to align
its API with POSIX diff and diffs on most systems exit with 1 when the
diff is not empty. Keep exiting with 0 when it is.

Fixes #66.

playground/__tests__/cli.test.js

@@ -26,4 +26,16 @@ describe('Test the config-sync CLI', () => {
     const { stdout } = await exec('yarn cs diff');
     expect(stdout).toContain('No differences between DB and sync directory');
   });
+  test('Non-empty diff returns 1', async () => {
+    await exec('rm -rf config/sync/admin-role.strapi-author.json');
+    // Work around Jest not supporting custom error matching.
+    // https://github.com/facebook/jest/issues/8140
+    let error;
+    try {
+      await exec('yarn cs diff');
+    } catch(e) {
+     error = e;
+    }
+    expect(error).toHaveProperty('code', 1);
+  });
 });

server/cli.js

@@ -269,7 +269,7 @@ program
         { color: true },
       ));
 
-      process.exit(0);
+      process.exit(1);
     }
 
     // Init table.
@@ -283,7 +283,7 @@ program
     // Print table.
     console.log(table.toString());
 
-    process.exit(0);
+    process.exit(1);
   });
 
 program.parseAsync(process.argv);