Add Are They All True as a ruby til.

ruby/are-they-all-true.md

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+# Are They All True?
+
+There is a method on `Enumerable` that allows you to check against
+everything in a collection. This is the `all?` method.
+For instance, if you want to check if an array of values are all
+true, you can call it without arguments:
+
+```ruby
+> [true, true, true].all?
+# true
+> [true, false, true].all?
+# false
+```
+
+You can also pass it a block which is helpful if you want to check an
+attribute or method on a collection of objects, like so:
+
+```ruby
+> employees.all?(&:salaried?)
+# true
+> [1,2,3,4,5].all?(&:odd?)
+# false
+```