Make == definition conditional

[timholy]

Julia nightly now has this method (JuliaLang/julia#35855), so we should check for it before defining it.

[codecov]

Codecov Report

Merging #6 into master will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master       #6   +/-   ##
=======================================
  Coverage   93.67%   93.67%           
=======================================
  Files           3        3           
  Lines         158      158           
=======================================
  Hits          148      148           
  Misses         10       10           

Impacted Files	Coverage Δ
src/MethodAnalysis.jl	93.33% <0.00%> (ø)

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