Relax UTCTime parser

It seems with the newer time package, `reads` is returning more than a
single element tuple,

```
λ> t = "2009-04-15 10:02:06 UTC"
λ> reads @UTCTime t
[(2009-04-15 10:02:06 UTC,""),(2009-04-15 10:02:06 UTC," UTC")]
```

Checking for a first element with no trailing characters gets the tests
passing again.

src/Database/Schema/Migrations/Filesystem.hs

@@ -175,6 +175,7 @@ fieldProcessors = [ ("Created", setTimestamp )
 setTimestamp :: FieldProcessor
 setTimestamp value m = do
   ts <- case readTimestamp value of
+          ((t, ""):_) -> Right t
           [(t, _)] -> return t
           _ -> fail "expected one valid parse"
   return $ m { mTimestamp = Just ts }