Fix Params case handling in the index, sort and where func

This means that you can now do:

```
{{ range where .Site.Pages "Params.MYPARAM" "foo" }}
```

common/para/para.go

@@ -37,8 +37,8 @@ type Runner interface {
 
 type errGroupRunner struct {
 	*errgroup.Group
-	w *Workers
-	ctx  context.Context
+	w   *Workers
+	ctx context.Context
 }
 
 func (g *errGroupRunner) Run(fn func() error) {
@@ -68,6 +68,6 @@ func (w *Workers) Start(ctx context.Context) (Runner, context.Context) {
 	return &errGroupRunner{
 		Group: g,
 		ctx:   ctx,
-		w:  w,
+		w:     w,
 	}, ctx
 }

common/para/para_test.go

@@ -15,6 +15,7 @@ package para
 
 import (
 	"context"
+	"runtime"
 	"sort"
 	"sync"
 	"sync/atomic"
@@ -25,6 +26,9 @@ import (
 )
 
 func TestPara(t *testing.T) {
+	if runtime.NumCPU() < 4 {
+		t.Skipf("skip para test, CPU count is %d", runtime.NumCPU())
+	}
 
 	c := qt.New(t)