fix: do not run platform sensitive tests in doc

The doc gives a very good example of how one can ignore tests
depending on the platform it's running on. But when we check
this part of the doc, depending on the platform we're doing
it, we don't get the same output, hence the doc_test fails
on mac and succeeds on linux.

So to ensure doc test is portable we just don't check this
part of the doc.

Author: pgrange

README.adoc

@@ -667,7 +667,7 @@ If _condition_ is true, will skip all the tests in the current file which match
 
 This can be useful when one has tests that are dependent on system environment, for instance:
 
-```test
+```
 skip_if "uname | grep Darwin" linux
 skip_if "uname | grep Linux" darwin
 
@@ -681,7 +681,7 @@ test_darwin_proc_does_not_exist() {
 
 will output, on a Linux system:
 
-```output
+```
 	Running test_darwin_proc_does_not_exist ... SKIPPED
 	Running test_linux_proc_exists ... SUCCESS
 ```