Fix sigil symbol deprecation warning in v0.12.5+

As of v0.12.5, using % for sigils [is deprecated][1]. The ~ character
should be used instead. This change fixes up various tests and example
files such that they won't throw the deprecation warning.

[1]: https://github.com/elixir-lang/elixir/releases/tag/v0.12.5
Merge pull request #4 from andrewsardone/fix-sigil-deprecation-warning

Fix sigil symbol deprecation warning in v0.12.5+