Add VERSION check to be compatible with Julia v1.5+

[nickrobinson251]

right now, if used on Julia v1.5 (which is as yet unreleased), you get something like

WARNING: Method definition startswith(Any) in module Base at strings/util.jl:128 overwritten in module Wrangling at /home/pkgeval/.julia/packages/Wrangling/XBqSn/src/symbol_searching.jl:42.
  ** incremental compilation may be fatally broken for this module **

WARNING: Method definition endswith(Any) in module Base at strings/util.jl:113 overwritten in module Wrangling at /home/pkgeval/.julia/packages/Wrangling/XBqSn/src/symbol_searching.jl:42.
  ** incremental compilation may be fatally broken for this module **

WARNING: both Wrangling and Base export "contains"; uses of it in module Main must be qualified
basic varients: Error During Test at /home/pkgeval/.julia/packages/Wrangling/XBqSn/test/symbol_searching.jl:50
  Got exception outside of a @test
  UndefVarError: contains not defined

• see e.g. https://github.com/JuliaCI/NanosoldierReports/blob/18bb6d85b20e25f1a9f2f312963f4b8b4fe7082e/pkgeval/by_hash/a340bf1_vs_3c50b7f/logs/Wrangling/1.5.0-DEV-fc8aa8666a.log
• This is because things from this package are now in Base (following contains PR https://github.com/JuliaLang/julia/pull/35132 and endswith/startswith PR https://github.com/JuliaLang/julia/pull/35052)
• So to help with getting v1.5 out the door, we should just add a check along the lines of if VERSION < 1.5 to our code.
• We should also do #14