Add: rules/go_unknown_command for misspelled go commands. (#933)

* - Add: rules/go_unknown_command for misspelled go commands.
- Add: tests/test_go_unknown_command which tests match and mismatch case of rules/go_unknown_command.
- Change: Added description of go_unknown_command to README.md.

* Add: test_get_new_command for testing rules.go_unknown_command.test_get_new_command method.

* Change: go_unknown_command.match now uses for_app decorator.

* Add: get_golang_commands which dynamically gets golang possible commands.

* Fix: cache proper function instead of its result.

thefuck/rules/go_unknown_command.py

@@ -0,0 +1,28 @@
+from itertools import dropwhile, islice, takewhile
+import subprocess
+
+from thefuck.utils import get_closest, replace_argument, for_app, which, cache
+
+
+def get_golang_commands():
+    proc = subprocess.Popen('go', stderr=subprocess.PIPE)
+    lines = [line.decode('utf-8').strip() for line in proc.stderr.readlines()]
+    lines = dropwhile(lambda line: line != 'The commands are:', lines)
+    lines = islice(lines, 2, None)
+    lines = takewhile(lambda line: line, lines)
+    return [line.split(' ')[0] for line in lines]
+
+
+if which('go'):
+    get_docker_commands = cache(which('go'))(get_golang_commands)
+
+
+@for_app('go')
+def match(command):
+    return 'unknown command' in command.output
+
+
+def get_new_command(command):
+    closest_subcommand = get_closest(command.script_parts[1], get_golang_commands())
+    return replace_argument(command.script, command.script_parts[1],
+                            closest_subcommand)