Fix language in cpanm error message

@kappa thanks a lot for helping to improve the messaging in DuckPAN. After reading your changes I felt the message could still be improved a lot more and arrived at this:

```perl
sub cpanminus_install_error {
	shift->app->print_text(
		"[ERROR] Failure on installation of modules!",
		"There are several possible explanations and fixes for this error:",
		"1. The download from CPAN was unsuccessful - Please restart this installer.",
		"2. Some other error occured - Please read the `build.log` mentioned in the errors and see if you can fix the problem yourself.",
		"If you are unable to solve the problem, please let us know by making a GitHub Issue in the DuckPAN Repo:",
		"https://github.com/duckduckgo/p5-app-duckpan/issues",
		"Make sure to attach the `build.log` file if it exists, otherwise copy/paste the output you see."
	);
}
```

What do you think?