Feature(tonic-build): set tonic-build.build_server(false), do not build Server code. (#22)

diff --git a/build.rs b/build.rs
index 157d3d4..5c56668 100644
--- a/build.rs
+++ b/build.rs
@@ -15,7 +15,7 @@
 //
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
-    tonic_build::configure().compile(
+    tonic_build::configure().build_server(false).compile(
         &["./skywalking-data-collect-protocol/language-agent/Tracing.proto"],
         &["./skywalking-data-collect-protocol"],
     )?;