Redeclared section line was one off

Test plan:
* Have two section headings,
  verify error message of the
  first redeclaration is not
  off by one anymore.

internal/pkg/parse/capture.go

@@ -42,7 +42,7 @@ func (s *sectionedTemplate) checkValidHeadings(capturedSections []capturedSectio
 		}
 
 		for _, headingSourceLineIndex := range headingSourceLineIndexes[1:] {
-			s.setFatalMessage(fmt.Sprintf("Section %s on line %d redeclared", heading, headingSourceLineIndexes[0]), headingSourceLineIndex)
+			s.setFatalMessage(fmt.Sprintf("Section %s on line %d redeclared", heading, headingSourceLineIndexes[0]+1), headingSourceLineIndex)
 		}
 	}
 }