Update Use of Dialyzer in README (#713) 📑

📄 There is no longer a task for `mix dialyzer.plt`. The PLT is now built
by the process which runs with the `mix dialyzer` task. This change
removes the note from the README file to run `mix dialyzer.plt`.

🙈 The latest run of `mix dialyzer` created a new local file named
`.dialyzer.plt.hash`. This change adds the file to `.gitignore`.

.gitignore

@@ -20,6 +20,7 @@ npm-debug.log
 *.sublime-workspace
 *.sublime-project
 .dialyzer.plt
+.dialyzer.plt.hash
 
 screenshots
 /config/*.secret.exs

README.md

@@ -76,9 +76,9 @@ Run `mix test`
 
 ## Static Analysis
 
-Run `mix dialyzer.plt` to build the lookup table for static analysis. Then run
-`mix dialyzer` to run analysis. If your dependencies or your elixir version
-change, delete `.dialyzer.plt` and run `mix dialyzer.plt` to rebuild it.
+Run `mix dialyzer` to run the analysis. The lookup table will be created by this
+process. If your dependencies or your elixir version change, delete
+`.dialyzer.plt` and run `mix dialyzer.plt` to rebuild it.
 
 There are still a lot of warnings that are not fixable, but occasionally some
 real errors are found by dialyzer