fixed file locked error

After compiling on my machine and downloading a twitter user a second time, I get an error that the file locked. 
Changed file loading to strict evaluation to avoid this.

$ ./hs-twitterarchiver pontifex
Could not read archive file.
pontifex.json: openFile: does not exist (No such file or directory)
Fetching tweets from http://api.twitter.com/1/statuses/user_timeline/pontifex.json?count=200&page=1
Fetched 0 tweets
Writing to archive file
$ ./hs-twitterarchiver pontifex
Reading archive file
Fetching tweets from http://api.twitter.com/1/statuses/user_timeline/pontifex.json?count=200&page=1
Fetched 0 tweets
Writing to archive file
hs-twitterarchiver: pontifex.json: openFile: resource busy (file is locked)