Resolve SublimeLinter depreciations. Document need for Dockerfile syntax

.python-version

@@ -0,0 +1 @@
+3.8

README.md

@@ -20,6 +20,10 @@ Before installing this plugin, you must ensure that `dockerfilelint` is installe
 
 **Note:** This plugin requires `dockerfilelint` 1.4.0 or later.
 
+You must also install the Dockerfile syntax definitions available for Sublime Text under package control. Search for Dockerfile Syntax Highlighting.
+
+https://packagecontrol.io/packages/Dockerfile%20Syntax%20Highlighting
+
 ### Linter configuration
 In order for `dockerfilelint` to be executed by SublimeLinter, you must ensure that its path is available to SublimeLinter. Before going any further, please read and follow the steps in [“Finding a linter executable”](http://sublimelinter.readthedocs.org/en/latest/troubleshooting.html#finding-a-linter-executable) through [“Validating your PATH”](http://www.sublimelinter.com/en/latest/troubleshooting.html#validating-your-path) in the documentation.
 

linter.py

@@ -16,30 +16,24 @@
 
 class Dockerfilelint(Linter):
     """Provides an interface to dockerfilelint."""
-
-    syntax = 'dockerfile'
     cmd = 'dockerfilelint --json'
-    executable = 'dockerfilelint'
-    version_args = '--version'
-    version_re = r'(?P<version>\d+\.\d+\.\d+)'
-    version_requirement = '>= 1.4.0'
-    config_file = ('.dockerfilelintrc', '~')
 
     # The following regex parses text in format <file>:<line>:<error>:<message>\n
     #
     # Possible Bug & Deprecation marked as errors
     #
     # Optimization & Clarity marked as warnings
-
     regex = (
         r'^.+?:(?P<line>\d+):'
         r'(?:(?P<error>Possible Bug|Deprecation|)|(?P<warning>Optimization|Clarity|)):'
         r'(?P<message>.+)$\r?\n'
     )
+
     multiline = True
     error_stream = util.STREAM_STDOUT
-    selectors = {}
-    defaults = {}
+    defaults = {
+        'selector': 'source.dockerfile'
+    }
 
     def run(self, cmd, code):
         output = super().run(cmd, code)