Adjust composer files and app core min-version for 'drop PHP 5.6'

[phil-davis]

• adjust local composer files to PHP 7.0.8
• bump app core min-version to 10.2

because the app is now being tested only against core stable10 upcoming 10.2 that has dropped PHP 5.6 support.

[codecov]

Codecov Report

Merging #99 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master     #99   +/-   ##
========================================
  Coverage      31.2%   31.2%           
  Complexity       65      65           
========================================
  Files             6       6           
  Lines           250     250           
========================================
  Hits             78      78           
  Misses          172     172

---

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[codecov]

Codecov Report

Merging #99 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master     #99   +/-   ##
========================================
  Coverage      31.2%   31.2%           
  Complexity       65      65           
========================================
  Files             6       6           
  Lines           250     250           
========================================
  Hits             78      78           
  Misses          172     172

---

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 66fcc10...2b81ce6. Read the comment docs.