In dash interp jobs -r is not supported, so cutting it off (#58)

Small fix, since `dash` doesn't really like `jobs -r`. Also if we will use only `-p` - it will display the same pid's even when they are completed, so calling the full jobs afterwards to flush the done jobs.

build.sh

@@ -69,8 +69,11 @@ fi
 # Run parallel builds but no more than limit (gox doesn't support all the os/archs we need)
 pwait() {
     # Note: Dash really don't like jobs to be executed in a pipe or in other shell, soooo...
-    # Using "-p" to show only PIDs (because it could be multiline) and "-r" to show only running jobs
-    while jobs -pr > /tmp/jobs_list.tmp; do
+    # Using "jobs -p" to show only PIDs (because it could be multiline)
+    # Unfortunately "jobs -r" is not supported in dash, not a big problem with sleep for 1 sec
+    while jobs -p > /tmp/jobs_list.tmp; do
+        # Cleanup jobs list, otherwise "jobs -p" will stay the same forever
+        jobs > /dev/null 2>&1
         [ $(cat /tmp/jobs_list.tmp | wc -l) -ge $1 ] || break
         sleep 1
     done