Fix atf-sh(3) manpage issues

- Fix spelling errors (specifiying -> specifying) [1]
- Escape '.' at start of lines using & to tell the roff processor
  that the line isn't meant to be treated as a command [2].

Bump .Dd for the change

MFC after:	1 week
Reported by:	igor [1], manlint [2]
Sponsored by:	Dell EMC Isilon

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

@@ -22,7 +22,7 @@
 .\" IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 .\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 .\" IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-.Dd October 13, 2014
+.Dd March 6, 2017
 .Dt ATF-SH 3
 .Os
 .Sh NAME
@@ -129,7 +129,7 @@ tc2_cleanup() {
     ... second test case's cleanup ...
 }
 
-.Ns ... additional test cases ...
+\&... additional test cases ...
 
 atf_init_test_cases() {
     atf_add_test_case tc1
@@ -144,7 +144,7 @@ described in
 .Xr atf-test-case 4 .
 To define test cases, one can use the
 .Nm 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
@@ -334,7 +334,7 @@ atf_init_test_cases() {
 This other example shows how to include a file with extra helper functions
 in the test program:
 .Bd -literal -offset indent
-.Ns ... definition of test cases ...
+\&... definition of test cases ...
 
 atf_init_test_cases() {
     . $(atf_get_srcdir)/helper_functions.sh