(IAC-1228) Remove '+' from shell_join_spec test data

Prior to this commit, the `spec/functions/shell_join_spec.rb` tests
were failing on Ruby 2.7 as the `Shellwords.shelljoin` method in
2.7 does not escape the `+` character.

Rather than have specific datasets for Ruby versions `< 2.7` and
`>= 2.7`, it seemed easiest to simply remove this character from
the tests.

Author: Ciaran McCrisken

spec/functions/shell_escape_spec.rb

@@ -17,8 +17,8 @@
     it { is_expected.to run.with_params('foo').and_return('foo') }
     it { is_expected.to run.with_params('foo bar').and_return('foo\ bar') }
     it {
-      is_expected.to run.with_params('~`!@#$%^&*()_+-=[]\{}|;\':",./<>?')
-                        .and_return('\~\`\!@\#\$\%\^\&\*\(\)_\+-\=\[\]\\\\\{\}\|\;\\\':\",./\<\>\?')
+      is_expected.to run.with_params('~`!@#$%^&*()_-=[]\{}|;\':",./<>?')
+                        .and_return('\~\`\!@\#\$\%\^\&\*\(\)_-\=\[\]\\\\\{\}\|\;\\\':\",./\<\>\?')
     }
   end
 

spec/functions/shell_join_spec.rb

@@ -14,8 +14,8 @@
     it { is_expected.to run.with_params(['foo', 'bar']).and_return('foo bar') }
     it { is_expected.to run.with_params(['foo', 'bar baz']).and_return('foo bar\ baz') }
     it {
-      is_expected.to run.with_params(['~`!@#$', '%^&*()_+-=', '[]\{}|;\':"', ',./<>?'])
-                        .and_return('\~\`\!@\#\$ \%\^\&\*\(\)_\+-\= \[\]\\\\\{\}\|\;\\\':\" ,./\<\>\?')
+      is_expected.to run.with_params(['~`!@#$', '%^&*()_-=', '[]\{}|;\':"', ',./<>?'])
+                        .and_return('\~\`\!@\#\$ \%\^\&\*\(\)_-\= \[\]\\\\\{\}\|\;\\\':\" ,./\<\>\?')
     }
 
     context 'with UTF8 and double byte characters' do