Make typecheck default parallelism 3

Typecheck is still hitting memory limits semi-regularly on periodic CI
jobs. This bumps the default parallelism down to 3 from 4 to make it
slightly less memory intensive.

Signed-off-by: hasheddan <georgedanielmangum@gmail.com>

test/typecheck/main.go

@@ -39,7 +39,7 @@ var (
 	timings    = flag.Bool("time", false, "output times taken for each phase")
 	defuses    = flag.Bool("defuse", false, "output defs/uses")
 	serial     = flag.Bool("serial", false, "don't type check platforms in parallel (equivalent to --parallel=1)")
-	parallel   = flag.Int("parallel", 4, "limits how many platforms can be checked in parallel. 0 means no limit.")
+	parallel   = flag.Int("parallel", 3, "limits how many platforms can be checked in parallel. 0 means no limit.")
 	skipTest   = flag.Bool("skip-test", false, "don't type check test code")
 	tags       = flag.String("tags", "", "comma-separated list of build tags to apply in addition to go's defaults")
 	ignoreDirs = flag.String("ignore-dirs", "", "comma-separated list of directories to ignore in addition to the default hardcoded list including staging, vendor, and hidden dirs")