install protoc

taken from PR SpinResearch#74

Author: mbrysa

.travis.yml

@@ -48,3 +48,8 @@ script:
   - cargo build --verbose --all-features
   - cargo test --verbose --all-features
   - cargo doc --verbose --all-features
+
+before_install:
+  - export PATH=$PATH:$HOME/protobuf/bin
+  - export PROTOC_VERSION=$(cat PROTOC_VERSION)
+  - bash install_protobuf.sh

PROTOC_VERSION

@@ -0,0 +1 @@
+3.11.3

install_protobuf.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+set -e
+set -x
+
+PROTOC_VERSION=$(cat PROTOC_VERSION)
+
+check_protoc_version () {
+    this_version=`protoc --version`
+    return `[ "libprotoc $PROTOC_VERSION" = "$this_version" ]`
+}
+
+if check_protoc_version; then
+    echo $PROTOC_VERSION detected.
+    exit
+fi
+
+wget https://github.com/google/protobuf/archive/v$PROTOC_VERSION.tar.gz
+tar -xzf v$PROTOC_VERSION.tar.gz
+cd protobuf-$PROTOC_VERSION
+./autogen.sh >/dev/null 2>&1
+./configure --prefix=$HOME/protobuf >/dev/null 2>&1
+make >/dev/null 2>&1
+make install >/dev/null 2>&1