Sqlite version in README

I've tested example database creation using README and encountered a few problem during the process:

1. There is missing ; at the end of scheme.sql causing error:

   Incomplete SQL: ...

2. After adding missing ; there was a problem with IF NOT EXISTS statement at the first line causing error:

   SQL error: near "NOT": syntax error

   Even though everything seems to be correct the only solution was to remove IF NOT EXISTS

3. With the two mentioned corrections applied I tried to run ca.py which ended up with:

   Traceback (most recent call last):
       File "ca.py", line 14, in <module>
           main()
       File "ca.py", line 10, in main
           sentinel_ca.run()
       File ".../ca/sentinel_ca/main.py", line 72, in run
           db = init_db(conf)
       File ".../ca/sentinel_ca/db.py", line 22, in init_db
           """)
   sqlite3.DatabaseError: file is encrypted or is not a database

All the problems could be solved by using sqlite3 instead of sqlite on the command line

I've been using:

• python3 ver. 3.5.3
• python-sqlite3 ver. 2.6.0
• sqlite 2.8.17
• sqlite3 3.16.2
• Debian Stretch

Please either correct the files or even better - add the working version of mentioned packages/programs to the README.