Typo in version number

3.10 -> 3.1
diff --git a/compiler/Dockerfile b/compiler/Dockerfile
index b04c0c3..af3036e 100644
--- a/compiler/Dockerfile
+++ b/compiler/Dockerfile
@@ -2,7 +2,7 @@
 
 RUN scl enable devtoolset-1.1 'bash -c "cd /protobuf && \
     git fetch && \
-    git checkout v3.10 && \
+    git checkout v3.1.0 && \
     ./autogen.sh && \
     CXXFLAGS=-m32 ./configure --disable-shared --prefix=/protobuf-32 && \
     make clean && make -j$(nproc) && make -j$(nproc) install"'