Remove 3 `tonumber` to erase the i64 not supported in Lua issue. (#11)

* Remove 3 `tonumber` to erase the i64 not supported in Lua issue.

* Fix span test case

* Fix segment ref test cases.
diff --git a/lib/skywalking/segment_ref_test.lua b/lib/skywalking/segment_ref_test.lua
index 1e854c6..94fc0c0 100644
--- a/lib/skywalking/segment_ref_test.lua
+++ b/lib/skywalking/segment_ref_test.lua
@@ -25,8 +25,8 @@
     function TestSegmentRef:testFromSW6Value()
         local ref = SegmentRef:new():fromSW6Value('1-My40LjU=-MS4yLjM=-4-1-1-IzEyNy4wLjAuMTo4MDgw-Iy9wb3J0YWw=-MTIz')
         lu.assertNotNil(ref)
-        lu.assertEquals(ref.trace_id, {3, 4, 5})
-        lu.assertEquals(ref.segment_id, {1, 2, 3})
+        lu.assertEquals(ref.trace_id, {"3", "4", "5"})
+        lu.assertEquals(ref.segment_id, {"1", "2", "3"})
         lu.assertEquals(ref.span_id, 4)
         lu.assertEquals(ref.parent_service_instance_id, 1)
         lu.assertEquals(ref.entry_service_instance_id, 1)
diff --git a/lib/skywalking/span_test.lua b/lib/skywalking/span_test.lua
index d70be81..274f3cc 100644
--- a/lib/skywalking/span_test.lua
+++ b/lib/skywalking/span_test.lua
@@ -48,10 +48,10 @@
         lu.assertEquals(span1.layer, SpanLayer.NONE)
         local ref = span1.refs[1]
         lu.assertNotNil(ref)
-        lu.assertEquals(ref.trace_id, {3, 4, 5})
+        lu.assertEquals(ref.trace_id, {"3", "4", "5"})
         -- Context trace id will be overrided by the ref trace id
-        lu.assertEquals(context.trace_id, {3, 4, 5})
-        lu.assertEquals(ref.segment_id, {1, 2, 3})
+        lu.assertEquals(context.trace_id, {"3", "4", "5"})
+        lu.assertEquals(ref.segment_id, {"1", "2", "3"})
         lu.assertEquals(ref.span_id, 4)
         lu.assertEquals(ref.parent_service_instance_id, 1)
         lu.assertEquals(ref.entry_service_instance_id, 1)
diff --git a/lib/skywalking/util.lua b/lib/skywalking/util.lua
index 8a349fa..18fe0ba 100644
--- a/lib/skywalking/util.lua
+++ b/lib/skywalking/util.lua
@@ -98,10 +98,6 @@
         return nil
     end
 
-    parts[1] = tonumber(parts[1])
-    parts[2] = tonumber(parts[2])
-    parts[3] = tonumber(parts[3])
-
     return parts
 end