Update phpstan/phpstan requirement from 1.0.0 to 1.2.0 (#61)

Updates the requirements on [phpstan/phpstan](https://github.com/phpstan/phpstan) to permit the latest version.
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Changelog](https://github.com/phpstan/phpstan/blob/master/CHANGELOG.md)
- [Commits](phpstan/phpstan@1.0.0...1.2.0)

---
updated-dependencies:
- dependency-name: phpstan/phpstan
  dependency-type: direct:development
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

composer.json

@@ -8,7 +8,7 @@
 		"php-64bit": "*"
 	},
 	"require-dev": {
-		"phpstan/phpstan": "1.0.0",
+		"phpstan/phpstan": "1.2.0",
 		"phpstan/extension-installer": "^1.0",
 		"phpstan/phpstan-strict-rules": "^1.0.0"
 	},