Put a spacer between LHS and RHS lines printed

Width calculations already consider the spacer, but it was lost in a
refactor.

CHANGELOG.md

@@ -22,6 +22,8 @@ indentation changes.
 Improved alignment for lines at the beginning of a changed group of
 lines.
 
+Improved horizontal spacing between before and after code shown.
+
 ### Command Line Interface
 
 Removed unused `--inline` and `--context` arguments.

src/lines.rs

@@ -400,6 +400,8 @@ fn apply_group(
                 result.push_str(&" ".repeat(lhs_content_width));
             }
         }
+        result.push_str(SPACER);
+
         match rhs_line_num {
             Some(rhs_line_num) => {
                 result.push_str(&format_line_num_padded(rhs_line_num.0, rhs_column_width));