Fix source code indexing on 0.6

I had changed this to work around #24586 on 0.7, but it turns out that
on 0.6, broadcast returned a vector, introducing the very problem there
that we were trying to avoid on 0.7. Fix that by just doing the addition
on the start/end of the range.

Fixes #9

Author: Keno

src/DebuggerFramework.jl

@@ -159,7 +159,7 @@ module DebuggerFramework
         current_line = line
         stoplinelength = length(string(stopline))
 
-        code = split(code[broadcast(+, startoffset:stopoffset, 1)],'\n')
+        code = split(code[(startoffset+1):(stopoffset+1)],'\n')
         lineno = startline
 
         if !isempty(code) && isempty(code[end])