Conjoin matchinglines

gistfile1.txt

input:

["15:19",
"< rektide>",
....
....
....
....],
["15:20",
"< rektide>",
....
....
....],

output:

["15:19", "< rektide>",
....
....
....
....],
["15:20", "< rektide>",
....
....
...],


guesswork at a means:
:s/^\[(.*?),\r(.*?)\r/[$1, $2/gn 10000

description of guesswork's selection and dump:

select:
beginning of a line, look for a [, the rest of the line, a comma, a newline, the next line. 
two lines, any starting with [ ends with , and the one that follows

dump:
one line with both of the previous lines joined together.