fix: use IP for metadata server

[JustinBeckwith]

This is coming up in:

• Cloud Run Cold Starts to Datastore Take Tens of Seconds nodejs-datastore#481
• Cloud Run metadata lag cloud-trace-nodejs#1114

DNS was probably a mistake

[codecov]

Codecov Report

Merging #233 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #233   +/-   ##
=======================================
  Coverage   89.25%   89.25%           
=======================================
  Files           1        1           
  Lines         121      121           
  Branches       28       28           
=======================================
  Hits          108      108           
  Misses         12       12           
  Partials        1        1

Impacted Files	Coverage Δ
src/index.ts	89.25% <100%> (ø)	⬆️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

Merging #233 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #233   +/-   ##
=======================================
  Coverage   89.25%   89.25%           
=======================================
  Files           1        1           
  Lines         121      121           
  Branches       28       28           
=======================================
  Hits          108      108           
  Misses         12       12           
  Partials        1        1

Impacted Files	Coverage Δ
src/index.ts	89.25% <100%> (ø)	⬆️

---

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 63bcb6d...5c850e1. Read the comment docs.