fix: bump node version on Dockerfile to be on par with docker-compose

[fguarini]

SUMMARY

Bump node version used on Dockerfile from '10-jessie' to '12' so it's on par with docker-compose

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TEST PLAN

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

[codecov-commenter]

Codecov Report

Merging #10813 into master will decrease coverage by 0.10%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #10813      +/-   ##
==========================================
- Coverage   61.23%   61.12%   -0.11%     
==========================================
  Files         802      802              
  Lines       37815    37815              
  Branches     3557     3557              
==========================================
- Hits        23155    23116      -39     
- Misses      14474    14513      +39     
  Partials      186      186              

Flag	Coverage Δ
#javascript	61.62% <ø> (ø)
#python	60.83% <ø> (-0.17%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/db_engine_specs/presto.py	73.54% <0.00%> (-8.75%)	⬇️
superset/examples/world_bank.py	97.10% <0.00%> (-2.90%)	⬇️
superset/examples/birth_names.py	97.36% <0.00%> (-2.64%)	⬇️
superset/models/core.py	88.05% <0.00%> (-0.28%)	⬇️
superset/connectors/sqla/models.py	89.61% <0.00%> (-0.14%)	⬇️
superset/sql_lab.py	78.69% <0.00%> (+0.43%)	⬆️
superset/result_set.py	98.34% <0.00%> (+1.65%)	⬆️
superset/db_engine_specs/sqlite.py	75.00% <0.00%> (+9.37%)	⬆️

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