Docker killed by system during assembly

Question

I am trying to build my project on a digital ocean droplet using the command:

docker-compose -f dev.yml build

Login to the console:

Building node
Step 1/5 : FROM node:6.9.2
 ---> faaadb4aaf9b
Step 2/5 : COPY ./compose/node/entrypoint-dev.sh /entrypoint.sh
 ---> Using cache
 ---> 6c22978494e4
Step 3/5 : RUN sed -i 's/\r//' /entrypoint.sh     && chmod +x /entrypoint.sh
 ---> Running in d7e663ef224c
Killed

I thought the problem was in memory, so I created a swap with the commands:

SWAPFILE=/swapfile [ =   /  ] 
touch $SWAPFILE
chmod 600 $SWAPFILE
# TODO: pass "count" param to script as argument
dd if=/dev/zero of=$SWAPFILE bs=1024k count=2000
mkswap $SWAPFILE
swapon $SWAPFILE

So, swap was created, but I still get Killed information when I try to build docker. Why?