add stauts_code (#41)

diff --git a/lib/skywalking/tracer.lua b/lib/skywalking/tracer.lua
index af0cdc6..9803337 100644
--- a/lib/skywalking/tracer.lua
+++ b/lib/skywalking/tracer.lua
@@ -77,6 +77,7 @@
     local TC = require('tracing_context')
     local Segment = require('segment')
     if ngx.ctx.entrySpan ~= nil then
+        Span.tag(ngx.ctx.entrySpan, 'http.status', ngx.var.status)
         Span.finish(ngx.ctx.entrySpan, ngx.now() * 1000)
         local status, segment = TC.drainAfterFinished(ngx.ctx.tracingContext)
         if status then
diff --git a/test/e2e/e2e-with-mock-collector/src/test/resources/expectedData.yaml b/test/e2e/e2e-with-mock-collector/src/test/resources/expectedData.yaml
index 49513ff..cb8f51c 100644
--- a/test/e2e/e2e-with-mock-collector/src/test/resources/expectedData.yaml
+++ b/test/e2e/e2e-with-mock-collector/src/test/resources/expectedData.yaml
@@ -42,6 +42,7 @@
             tags:
               - {key: http.method, value: GET}
               - {key: http.params, value: 'http://127.0.0.1/tier2/lb'}
+              - {key: http.status, value: '200'}
             endTime: gt 0
             spanType: Entry
             spanId: 0
@@ -71,6 +72,7 @@
             tags:
               - {key: http.method, value: GET}
               - {key: http.params, value: 'not null'}
+              - {key: http.status, value: '200'}
             endTime: gt 0
             spanType: Entry
             spanId: 0