Corrected [Tt]reshold to [Tr]hreshold

[SamuelHebert]

I believe I have found a typo in the module, multiple references are made to treshold but this should be threshold. Looking at https://help.ubuntu.com/community/Apt-Cacher%20NG

Tuning cache

ExThreshold: 4 # days before purgeing
ExStartTradeOff: 500m # Size of local cache, expiration run is suppressed, until limited is surpaced.

A quick search of the repo found the following entries:

shebert@shebert-lnx ~/projects/puppet-aptcacherng (production)$ grep -ri tres
spec/classes/aptcacherng_init_spec.rb:      it { is_expected.to contain_file('/etc/apt-cacher-ng/acng.conf').with_content(%r{^ExTreshold: 4$}) }
spec/classes/aptcacherng_init_spec.rb:          extreshold: 4,
spec/classes/aptcacherng_init_spec.rb:      it { is_expected.to contain_file('/etc/apt-cacher-ng/acng.conf').with_content(%r{^ExTreshold: #{params_set[:extreshold]}$}) }
templates/acng.conf.erb:ExTreshold: <%= @extreshold %>
manifests/init.pp:# [*extreshold*]
manifests/init.pp:  Integer                        $extreshold,
manifests/config.pp:  $extreshold = $aptcacherng::extreshold
README.md:* ExTreshold: 4
data/common.yaml:aptcacherng::extreshold: 4

I've updated the entries in quesiton.