Your transaction's fee is pretty high and its size is small. It usually should get confirmed right in the next block.
The reason it's still unconfirmed is that there currently is a very big number of unconfirmed transactions. Around 57'000. Usually, it's somewhere around 1'000 to 3'000.
This already happened a few months ago. The mempool back then was 8 MB big. Right now, it's 35 to 43 MB big (depending on who you ask) and a block being mined (which statistically happens every 10 minutes) can only reduce it by about 1 MB.
Inconveniently for you, the size of the mempool has skyrocketed since you made the transaction due increased frequency of transactions.
If it continues like this, the blocksize limit will likely be increased so a block can decrease the mempool by more than 1 MB.
Your fee (0.5907 mBTC/kB) is above the current mempool average (0.2871 mBTC/kB) but there are a lot of transactions with higher fees than yours. Because of this, the miners will pick other transactions instead of yours.
The only thing you can do if you really need the transaction to go through fast is to send it again with a higher fee, this time.