install pip for python 3 in ubuntu 18.04

$ sudo apt-get update
$ sudo apt-get upgrade
$ sudo apt-get install libssl-dev openssl libreadline-dev
$ cd ~
$ wget https://www.python.org/ftp/python/3.6.1/Python-3.6.1.tgz
$ tar zxf Python-3.6.1.tgz
$ cd Python-3.6.1
$ ./configure
$ make
$ sudo make install