Add skipped count tests in the summary

This also update the behaviour of the summary, now it only display the
number of failures, and skipped tests also, if the numbers are greater
than zero.

libexec/bats-format-tap-stream

@@ -11,6 +11,7 @@ if [[ "$header" =~ $header_pattern ]]; then
   count="${header:3}"
   index=0
   failures=0
+  skipped=0
   name=""
   count_column_width=$(( ${#count} * 2 + 2 ))
 else
@@ -64,9 +65,15 @@ log() {
 }
 
 summary() {
-  printf "\n%d test%s, %d failure%s\n" \
-    "$count" "$(plural "$count")" \
-    "$failures" "$(plural "$failures")"
+  printf "\n%d test%s" "$count" "$(plural "$count")"
+
+  printf ", %d failure%s" "$failures" "$(plural "$failures")"
+
+  if [ "$skipped" -gt 0 ]; then
+    printf ", %d skipped" "$skipped"
+  fi
+
+  printf "\n"
 }
 
 printf_with_truncation() {
@@ -139,6 +146,7 @@ while IFS= read -r line; do
   "ok "* )
     skip_expr="ok $index # skip (\(([^)]*)\))?"
     if [[ "$line" =~ $skip_expr ]]; then
+      let skipped+=1
       buffer skip "${BASH_REMATCH[2]}"
     else
       buffer pass