Further migration to Java 1.8

[david-russo]

This updates internal version checks, messages, and documentation to match the updated Java version requirement, and replaces a duplicate method with its Java 1.8 equivalent.

Closes #372

[codecov]

Codecov Report

Merging #343 into integration will decrease coverage by <.01%.
The diff coverage is 0%.

@@                Coverage Diff                @@
##             integration     #343      +/-   ##
=================================================
- Coverage          44.49%   44.48%   -0.01%     
+ Complexity          3418     3415       -3     
=================================================
  Files                368      368              
  Lines              30323    30321       -2     
  Branches            5988     5987       -1     
=================================================
- Hits               13491    13489       -2     
  Misses             14423    14423              
  Partials            2409     2409

Impacted Files	Coverage Δ	Complexity Δ
...du/harvard/hul/ois/jhove/CoreMessageConstants.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...a/edu/harvard/hul/ois/jhove/module/WaveModule.java	64.72% <0%> (-0.19%)	59 <0> (-3)
...main/java/edu/harvard/hul/ois/jhove/JhoveBase.java	40.88% <0%> (ø)	41 <0> (ø)	⬇️

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[carlwilson]

Good catch on the README, cheers.