Fix vendored dep because upstream is non-responsive

Eventually this needs to be fixed in the textflow project by Phil,
but he has not done so in the half a year this bug has been known
to be there, so...

Closes #1470
Closes #1455

third_party/clara.hpp

@@ -110,6 +110,9 @@ namespace clara { namespace TextFlow {
                 m_suffix = false;
                 auto width = m_column.m_width-indent();
                 m_end = m_pos;
+                if (line()[m_pos] == '\n') {
+                    ++m_end;
+                }
                 while( m_end < line().size() && line()[m_end] != '\n' )
                     ++m_end;