Restore CDAClient.Builder constructor modifier

Author: Tom Reznik

src/main/java/com/contentful/java/cda/CDAClient.java

@@ -284,7 +284,7 @@ public static class Builder {
     boolean secure;
     boolean nullifyUnresolved;
 
-    private Builder() {
+    public Builder() {
       // Defaults
       this.secure = true;
     }