Upgrade to protobuf-3.0.0-alpha-3
diff --git a/compiler/Dockerfile b/compiler/Dockerfile
index 4994f64..84df560 100644
--- a/compiler/Dockerfile
+++ b/compiler/Dockerfile
@@ -1,7 +1,7 @@
 FROM protoc-artifacts:latest
 
 RUN scl enable devtoolset-1.1 'bash -c "cd /protobuf && \
-    git checkout v3.0.0-alpha-2 && \
+    git checkout v3.0.0-alpha-3 && \
     ./autogen.sh && \
     CXXFLAGS=-m32 ./configure --disable-shared --prefix=/protobuf-32 && \
     make clean && make && make install"'
diff --git a/compiler/README.md b/compiler/README.md
index f9c6b6a..df4a5b1 100644
--- a/compiler/README.md
+++ b/compiler/README.md
@@ -13,7 +13,7 @@
 
 * Linux, Mac OS X with Clang, or Windows with MSYS2
 * Java 7 or up
-* [Protobuf](https://github.com/google/protobuf) 3.0.0-alpha-2 or up
+* [Protobuf](https://github.com/google/protobuf) 3.0.0-alpha-3 or up
 
 ## Compiling and testing the codegen
 Change to the `compiler` directory: