Fix `/proc/{pid}/stat` parsing: Allow thread names to contain )

[wmanley]

by finding the terminating ) by looking for the last one on the line, rather than the first one.

See https://stackoverflow.com/a/29887040/65031

We name our Python threads after the Thread's target function. The thread named Thre.(<lambda>) was causing py-spy to fail with: "Error: Failed to parse /proc/83/stat"

[benfred]

thanks for the fix! it looks good to me