Fix git log command redundant flags

* --pretty=online does not have any effect on presence of -L
* Fix specs to use more explicit wording / format preparing followup
  change

lib/mutant/repository.rb

@@ -49,7 +49,7 @@ module Mutant
       # @api private
       def touches?(path, line_range)
         command = %W[
-          git log --pretty=oneline
+          git log
           #{from}...#{to}
           -L #{line_range.begin},#{line_range.end}:#{path}
         ]

spec/unit/mutant/repository/diff_spec.rb

@@ -18,23 +18,26 @@ describe Mutant::Repository::Diff do
     subject { object.touches?(path, line_range) }
 
     before do
-      expect(Open3).to receive(:capture2).with(
-        *expected_command,
-        binmode: true
-      ).and_return([stdout, status])
+      expect(Open3).to receive(:capture2)
+        .ordered
+        .with(*expected_git_log_command, binmode: true)
+        .and_return([stdout, status])
     end
 
-    let(:expected_command) do
+    let(:expected_git_log_command) do
       %w[
-        git log --pretty=oneline from_rev...to_rev -L 1,2:foo.rb
+        git log from_rev...to_rev -L 1,2:foo.rb
       ]
     end
 
-    context 'on failure of git command' do
+    context 'on failure of git log command' do
       let(:success?) { false }
 
       it 'raises error' do
-        expect { subject }.to raise_error(Mutant::Repository::RepositoryError, "Command #{expected_command} failed!")
+        expect { subject }.to raise_error(
+          Mutant::Repository::RepositoryError,
+          "Command #{expected_git_log_command} failed!"
+        )
       end
     end