fix: Set storage update time in FakeStorageRpc

[hosainnet]

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

Fixes #173

[google-cla]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed (or fixed any issues), please reply here with @googlebot I signed it! and we'll verify it.

---

What to do if you already signed the CLA

Individual signers

• It's possible we don't have your GitHub username or you're using a different email address on your commit. Check your existing CLA data and verify that your email is set on your git commits.

Corporate signers

• Your company has a Point of Contact who decides which employees are authorized to participate. Ask your POC to be added to the group of authorized contributors. If you don't know who your Point of Contact is, direct the Google project maintainer to go/cla#troubleshoot (Public version).
• The email used to register you as an authorized contributor must be the email used for the Git commit. Check your existing CLA data and verify that your email is set on your git commits.
• The email used to register you as an authorized contributor must also be attached to your GitHub account.

ℹ️ Googlers: Go here for more info.

[hosainnet]

@googlebot I signed it!

[codecov]

Codecov Report

Merging #174 (8ce0ccd) into master (4e7bac1) will increase coverage by 0.50%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #174      +/-   ##
============================================
+ Coverage     71.71%   72.21%   +0.50%     
- Complexity      495      499       +4     
============================================
  Files            29       29              
  Lines          1658     1663       +5     
  Branches        268      268              
============================================
+ Hits           1189     1201      +12     
+ Misses          344      336       -8     
- Partials        125      126       +1     

Impacted Files	Coverage Δ	Complexity Δ
...ud/storage/contrib/nio/testing/FakeStorageRpc.java	71.42% <100.00%> (+3.97%)	47.00 <2.00> (+4.00)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4e7bac1...8ce0ccd. Read the comment docs.

[hosainnet]

@chingor13 @frankyn thanks!