Rakefile: reformat help task to work with rake 12.3.3

With rake 12.3.3, rake command fails as below

rake aborted!
SyntaxError: /root/lkp-tests/Rakefile:12: syntax error, unexpected ==, expecting keyword_end
  == SPEC ==
    ^
/root/lkp-tests/Rakefile:15: syntax error, unexpected ':', expecting keyword_end
/root/lkp-tests/Rakefile:17: syntax error, unexpected tSTRING_BEG, expecting keyword_do or '{' or '('
    rake spec spec=job"             # check spec/job_spec.rb status
                       ^
/root/lkp-tests/Rakefile:23: syntax error, unexpected tIDENTIFIER, expecting keyword_end
    rake rubocop file="lib/**/*.rb" # check all lib files
                          ^
/root/lkp-tests/Rakefile:35: syntax error, unexpected ',', expecting '}'
  t.pattern = "spec/**{,/*/**}/#{spec}_spec.rb"
                        ^
target of repeat operator is not specified: /*/
/root/lkp-tests/Rakefile:35: syntax error, unexpected '}'
  t.pattern = "spec/**{,/*/**}/#{spec}_spec.rb"
                              ^
/root/lkp-tests/Rakefile:89: syntax error, unexpected end-of-input, expecting keyword_end

Signed-off-by: Philip Li <[email protected]>

Rakefile

@@ -8,20 +8,22 @@ require 'English'
 desc 'Show help'
 task :help do
   puts <<~EOF
+  ## SPEC
 
-  == SPEC ==
+  usage
+    rake spec [spec=result_path]
 
-  usage: rake spec [spec=result_path]
-  example:
+  example
     rake spec                       # check all unit tests status
-    rake spec spec=job"             # check spec/job_spec.rb status
+    rake spec spec=job              # check spec/job_spec.rb status
 
-  == RUBOCOP ==
+  ## RUBOCOP
 
-  usage: rake rubocop [file=pattern]
-  example:
-    rake rubocop file="lib/**/*.rb" # check all lib files
+  usage
+    rake rubocop [file=pattern]
 
+  example
+    rake rubocop file="lib/**/*.rb" # check all lib files
   EOF
 end