move from File to Path types

[erdos]

Move from using the legacy java.io.File to java.nio.file.Path from the NIO2 update for the Java API.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Project coverage is 93.70%. Comparing base (1b6c38c) to head (96e9f6b).

Files with missing lines	Patch %	Lines
src/stencil/api.clj	50.00%	0 Missing and 2 partials :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #168      +/-   ##
==========================================
- Coverage   93.83%   93.70%   -0.14%     
==========================================
  Files          29       29              
  Lines        2092     2096       +4     
  Branches       92       95       +3     
==========================================
+ Hits         1963     1964       +1     
  Misses         37       37              
- Partials       92       95       +3     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

:rocket: New features to boost your workflow:

• :snowflake: Test Analytics: Detect flaky tests, report on failures, and find test suite problems.