Enable fatal warnings

[AlexITC]

Run sbt "++2.13.7" compile which throws these warnings:

[warn] /home/scala-js-chrome/bindings/src/main/scala/chrome/browserAction/bindings/BadgeBackgroundColorDetails.scala:14:74: Implicit resolves to enclosing value colorEvidence
[warn]   implicit val colorEvidence: Evidence[String | js.Array[Int], js.Any] = implicitly
[warn]                                                                          ^
[warn] /home/scala-js-chrome/bindings/src/main/scala/chrome/browserAction/bindings/IconDetails.scala:18:88: Implicit resolves to enclosing value imageEvidence
[warn]   implicit val imageEvidence: Evidence[ImageData | js.Dictionary[ImageData], js.Any] = implicitly
[warn]                                                                                        ^
[warn] /scala-js-chrome/bindings/src/main/scala/chrome/browserAction/bindings/IconDetails.scala:19:81: Implicit resolves to enclosing value pathEvidence
[warn]   implicit val pathEvidence: Evidence[String | js.Dictionary[String], js.Any] = implicitly
[warn]                                                                                 ^
[warn] three warnings found

Let's resolve the warnings and enable fatal warnings in the build.