Fix typo (#445)

LGTM
diff --git a/docs/en-us/dev/SPI.md b/docs/en-us/dev/SPI.md
index 0213237..4581c88 100644
--- a/docs/en-us/dev/SPI.md
+++ b/docs/en-us/dev/SPI.md
@@ -18,7 +18,7 @@
 
 ### Example:
 
-To extend Dubbo Protocol, placee a text file in the extension jar file: `META-INF/dubbo/org.apache.dubbo.rpc.Protocol`, content:
+To extend Dubbo Protocol, place a text file in the extension jar file: `META-INF/dubbo/org.apache.dubbo.rpc.Protocol`, content:
 
 ```properties
 xxx=com.alibaba.xxx.XxxProtocol