change source array to string

Status Job ID Name Coverage
  Stack
passed #10878
stack

00:03:53

 
  Cabal
failed #10879
cabal

00:29:05

 
  Bench
skipped #10880
bench
 
  Test
skipped #10881
test
 
Name Stage Failure
failed
cabal Cabal
   |
46 | , _hd_source = Just $ foldl (\x y -> x <> ", " <> y) "" (ISTEX._source_title s)
| ^
Error: cabal: Failed to build gargantext-0.0.6.9.9.9.4.4 (which is required by
exe:gargantext-upgrade from gargantext-0.0.6.9.9.9.4.4, exe:gargantext-server
from gargantext-0.0.6.9.9.9.4.4 and others).

Cleaning up file based variables
ERROR: Job failed: exit code 1