Downgrade node temporarily

[donatello]

To fix jest related build failure as recommended at jestjs/jest#8069 (comment)

[minio-ops]

Mint Automation

Test	Result
mint-compression-xl.sh	✔️
mint-xl.sh	✔️
mint-large-bucket.sh	✔️
mint-compression-dist-xl.sh	✔️
mint-compression-fs.sh	✔️
mint-worm.sh	✔️
mint-fs.sh	✔️
mint-dist-xl.sh	✔️
mint-gateway-nas.sh	✔️

[kaankabalak]

Seems like the frontend tests ran fine, approving...

https://travis-ci.org/minio/minio/jobs/502826030

[codecov]

Codecov Report

Merging #7333 into master will increase coverage by 0.46%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7333      +/-   ##
==========================================
+ Coverage   47.97%   48.44%   +0.46%     
==========================================
  Files         281      296      +15     
  Lines       46052    46384     +332     
==========================================
+ Hits        22095    22470     +375     
+ Misses      21902    21849      -53     
- Partials     2055     2065      +10

Impacted Files	Coverage Δ
cmd/os-reliable.go	65.65% <0%> (-2.03%)	⬇️
pkg/cgroup/linux.go	37.5% <0%> (ø)
cmd/posix-dirent-ino.go	100% <0%> (ø)
cmd/posix-list-dir_unix.go	75% <0%> (ø)
pkg/sys/rlimit-file_nix.go	100% <0%> (ø)
pkg/disk/type_linux.go	66.66% <0%> (ø)
pkg/ioutil/append-file_nix.go	66.66% <0%> (ø)
pkg/disk/root-disk-unix.go	0% <0%> (ø)
pkg/disk/stat_linux.go	84.61% <0%> (ø)
pkg/mountinfo/mountinfo_linux.go	75.38% <0%> (ø)
... and 23 more

---

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