Fix RuboCop errors

These errors were introduced when we increased the minimum Ruby version
to 3.x.

lib/slim_lint/file_finder.rb

@@ -72,7 +72,7 @@ def extract_files_from(patterns) # rubocop:disable Metrics/MethodLength
     # @param path [String]
     # @return [String]
     def normalize_path(path)
-      path.start_with?(".#{File::SEPARATOR}") ? path[2..-1] : path
+      path.start_with?(".#{File::SEPARATOR}") ? path[2..] : path
     end
 
     # Whether the given file should be treated as a Slim file.

lib/slim_lint/linter_registry.rb

@@ -27,11 +27,9 @@ def included(subclass)
       # @return [Array<Class>]
       def extract_linters_from(linter_names)
         linter_names.map do |linter_name|
-          begin
-            SlimLint::Linter.const_get(linter_name)
-          rescue NameError
-            raise NoSuchLinter, "Linter #{linter_name} does not exist"
-          end
+          SlimLint::Linter.const_get(linter_name)
+        rescue NameError
+          raise NoSuchLinter, "Linter #{linter_name} does not exist"
         end
       end
     end

slim_lint.gemspec

@@ -22,7 +22,7 @@ Gem::Specification.new do |s|
                        Dir['lib/**/*.rb'] +
                        ['LICENSE.md']
 
-  s.required_ruby_version = '>= 3'
+  s.required_ruby_version = '>= 3.0'
 
   s.add_runtime_dependency 'rubocop', ['>= 1.0', '< 2.0']
   s.add_runtime_dependency 'slim', ['>= 3.0', '< 6.0']

spec/slim_lint/engine_spec.rb

@@ -14,11 +14,9 @@
       end
 
       it 'includes the line number in the exception' do
-        begin
-          subject
-        rescue SlimLint::Exceptions::ParseError => e
-          e.lineno.should == 1
-        end
+        subject
+      rescue SlimLint::Exceptions::ParseError => e
+        e.lineno.should == 1
       end
     end