s/Modelling/Specification/ in CLI description

[orlade-anz]

Before:

ladeo@Olivers-MacBook-Pro sysl % sysl
usage: sysl [<flags>] <command> [<args> ...]

System Modelling Language Toolkit
[...]

After:

ladeo@Olivers-MacBook-Pro sysl % sysl
usage: sysl [<flags>] <command> [<args> ...]

System Specification Language Toolkit
[...]

Checklist:

• [ ] Added related tests
• [ ] Made corresponding changes to the documentation

[codecov[bot]]

Codecov Report

Merging #918 into master will increase coverage by 0.01%. The diff coverage is 78.33%.

@@            Coverage Diff             @@
##           master     #918      +/-   ##
==========================================
+ Coverage   83.35%   83.36%   +0.01%     
==========================================
  Files          73       73              
  Lines       10609    10653      +44     
==========================================
+ Hits         8843     8881      +38     
- Misses       1432     1437       +5     
- Partials      334      335       +1     

Impacted Files	Coverage Δ
pkg/mod/module.go	66.66% <33.33%> (+0.95%)	:arrow_up:
pkg/parse/listener_impl.go	89.59% <62.50%> (+0.08%)	:arrow_up:
pkg/mod/gomod.go	73.68% <66.66%> (+1.27%)	:arrow_up:
pkg/pbutil/output.go	76.00% <75.00%> (-0.48%)	:arrow_down:
pkg/importer/openapi.go	88.95% <80.00%> (-0.50%)	:arrow_down:
pkg/diagrams/diagutil.go	62.31% <100.00%> (ø)
pkg/importer/utils.go	88.23% <100.00%> (+0.35%)	:arrow_up:
...g/mermaid/integrationdiagram/integrationdiagram.go	86.66% <100.00%> (+2.29%)	:arrow_up: