Add upgrade notice on upgrading all Array types

Previously Vitrus implicitly coerced strings to integers when
Array[Integer] types were used. With dry-types, this is no longer done,
and APIs that expected this behavior will fail with an invalid type
check.  Expand the upgrade docs to include all Array types and an
example for Array[Integer].

Author: stanhu

UPGRADING.md

@@ -42,11 +42,11 @@ end
 
 Custom types which don't depend on Virtus don't require any changes.
 
-#### Ensure that Array[String] types have explicit coercions
+#### Ensure that Array types have explicit coercions
 
 Unlike Virtus, dry-types does not perform any implict coercions. If you
-have any uses of `Array[String]`, be sure they use a `coerce_with`
-block. For example:
+have any uses of `Array[String]`, `Array[Integer]`, etc. be sure they
+use a `coerce_with` block. For example:
 
 ```ruby
 requires :values, type: Array[String]
@@ -62,6 +62,12 @@ you might do:
 requires :values, type: Array[String], coerce_with: ->(val) { val.split(',').map(&:strip) }
 ```
 
+Likewise, for `Array[Integer]`, you might do:
+
+```ruby
+requires :values, type: Array[Integer], coerce_with: ->(val) { val.split(',').map(&:strip).map(&:to_i) }
+```
+
 For more information see [#1920](https://github.com/ruby-grape/grape/pull/1920).
 
 ### Upgrading to >= 1.2.4