Use stable version of SwiftLint

What's Changed

• Fix links to images in README by @valeriyvan in #162

Full Changelog: 1.2.0...1.2.1

What's Changed

• Turn on tests on Ubuntu, fix compile errors in tests by @valeriyvan in #125
• Fix/turn on tests on ubuntu by @valeriyvan in #126
• Extend Rgba with initializer from array, array slice, buffer and buffer slice by @valeriyvan in #129
• Add official SwiftLintBuildToolPlugin from SwiftLint package by @valeriyvan in #130
• Extend Bitmap with init with parameter ContiguousArray by @valeriyvan in #132
• Add to Rgba export to array and tuple; Add init from tuple by @valeriyvan in #136
• Implements initialising Bitmap from PPM string, export of Bitmap into PPM string by @valeriyvan in #137
• Extend Bitmap with initializer from UIImage and export to UIImage by @valeriyvan in #139
• Extend Bitmap with initializer form data of png/jpeg and export to png/jpeg by @valeriyvan in #143
• Add BitmapExporter to export geometrize result into Bitmap by @valeriyvan in #144
• Add to geometrize-cli ability to output png and jpeg by @valeriyvan in #146
• Add PrivacyInfo.xcprivacy by @valeriyvan in #147
• Rename geometrize-cli into geometrize by @valeriyvan in #148
• Fix for hang geometrizing image filled with solid color by @valeriyvan in #153
• Introduces GeometrizingSequence by @valeriyvan in #160
• Remove conformance to ExpressibleByStringLiteral and CustomStringConvertible, use PPM instead by @valeriyvan in #161
• Fix links to images in README by @valeriyvan in #162

Full Changelog: 1.1.6...1.2.1