Fix typos in flake8 test messages

Signed-off-by: Nick Diego Yamane <nick.diego@gmail.com>

test/command_callback/test_flake8_command_callback.vader

@@ -158,7 +158,7 @@ Execute(Using `python -m flake8` should be supported for running flake8):
   \ ale#Escape('python') . '   -m flake8 --some-option --format=default -',
   \ ale_linters#python#flake8#GetCommand(bufnr(''), ['2.9.9'])
 
-Execute(Using `python2 -m flake8` should be use with the old args option):
+Execute(Using `python2 -m flake8` should be supported with the old args option):
   let g:ale_python_flake8_executable = 'python2'
   let g:ale_python_flake8_args = '-m flake8'
   let g:ale_python_flake8_use_global = 0

test/handler/test_flake8_handler.vader

@@ -48,7 +48,7 @@ Execute(The flake8 handler should handle basic warnings and syntax errors):
   \   'stdin:8:3: E999 SyntaxError: invalid syntax',
   \ ])
 
-Execute(The flake8 handler should set end column indexes should be set for certain errors):
+Execute(The flake8 handler should set end column indexes for certain errors):
   AssertEqual
   \ [
   \   {