Fixing default value for insert param

* For boolean param JCommander by default interprets the option to have arity 0.
  Therefore a param is not specified for '--insert' option.
  If the option is provided the value is set to true. Hence setting the
  default param value to false.

src/main/java/com/thoughtworks/go/dbsync/cli/Args.java

@@ -55,7 +55,7 @@ public class Args {
     public String outputFile;
 
     @Parameter(names = {"--insert", "-i"}, description = "Perform INSERT into target database.", order = 1200)
-    public boolean insert = true;
+    public boolean insert = false;
 
     @Parameter(names = {"--progress", "-p"}, description = "Show progress of the export operation", order = 1300)
     public boolean progress = false;