gzip_disable "MSIE [1-6]\.";
gzip_buffers 16 32k;
gzip_min_length 1000: Minimum file size that should be compressed. If your file size is less than 1k, nginx will ignore your file.
gzip_buffers 16 8k: Sets the number and size of buffers used to compress a response. If the buffer size needed for your file is more than 8k, it might not work.