Fix issues with atf-check(1) found by igor and refer to atf-check(1)

- Fix typo (specifiying -> specifying)
- Add atf-check(1) to SEE ALSO section for completeness. It's mentioned
  above, but by convention the SEE ALSO section should list all relevant
  references to other tools and APIs.

Bump .Dd for the change

MFC after:	1 week
Sponsored by:	Dell EMC Isilon

contrib/atf/atf-sh/atf-sh-api.3

@@ -26,7 +26,7 @@
 .\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 .\" IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd March 2, 2014
+.Dd March 6, 2017
 .Dt ATF-SH-API 3
 .Os
 .Sh NAME
@@ -121,7 +121,7 @@ described in
 .Xr atf-test-case 4 .
 To define test cases, one can use the
 .Fn atf_test_case
-function, which takes a first parameter specifiying the test case's
+function, which takes a first parameter specifying the test case's
 name and instructs the library to set things up to accept it as a valid
 test case.
 The second parameter is optional and, if provided, must be
@@ -335,6 +335,7 @@ grep foo ls || atf_fail "foo file not found in listing"
 atf_check -s exit:0 -o match:"^foo$" -e empty 'ls'
 .Ed
 .Sh SEE ALSO
+.Xr atf-check 1 ,
 .Xr atf-sh 1 ,
 .Xr atf-test-program 1 ,
 .Xr atf-test-case 4