Adding two Vim-specific entries to .gitignore.

Vim creates a foo~ file after saving a file named foo with the old version.
Vim creates a .foo.swp file during an open edit session of a file named foo.
We (almost) never would want to add either of those to a Git repo.
Tests for user_name with integer or range argument

Adding tests of the optional argument to the Faker::Internet.user_name
method so that it assumes that if it is an integer it is specifying a
lower-bound to the length of the generated user name, and if it is a
range than it is a lower and upper bound to the length of the generated
user name.

For example:
  Faker::Internet.user_name 4
would never generate "abc" as a user name, but might generate "abcd".

Another example:
  Faker::Internet.user_name 4..8
would never generate "abc", might generate "abcd", might generate
"abcdefgh", but would never generate "abcdefghi".
Test fix: forgot to use .each.
Adding code to support integer arguments in user_name.

Adding code so that if you call Faker::Internet.user_name with an
integer, then it will insist that the generated user name is no shorter
in length than that.
Adding support to user_name for range specifiers.

If you now call Faker::Internet.user_name with a range as the optional
argument, then it will make sure that the generated user name is of a
length within that range.
Adding a test to confirm open ranges work correctly with user_name.
Merge branch 'login-lengths' of https://github.com/cgore/faker into cgore-login-lengths