Remove need for sudo

Not using sudo is a good thing: it reduces boot time from 20-52s to
1-6s.

See: https://docs.travis-ci.com/user/ci-environment/

Author: mbinna

.travis.yml

@@ -1,8 +1,5 @@
 # Source: https://github.com/boostorg/hana/blob/master/.travis.yml
 
-# Sudo is required for installing recent versions of dependencies.
-sudo: required
-
 # Use C++ build environment.
 language: cpp
 
@@ -32,8 +29,8 @@ install:
     # Install a recent version of the Protobuf
     - |
         PROTOBUF_URL="https://github.com/google/protobuf/releases/download/v3.2.0/protobuf-cpp-3.2.0.tar.gz"
-        if [ ! -f ${DEPS_DIR}/protobuf/src/.libs/protoc ] ; then mkdir -p protobuf ; travis_retry wget --no-check-certificate --quiet -O - ${PROTOBUF_URL} | tar --strip-components=1 -xz -C protobuf ; cd protobuf ; ./configure --prefix=/usr ; make ; else cd protobuf ; fi
-        sudo make install
+        if [ ! -f ${DEPS_DIR}/protobuf/src/.libs/protoc ] ; then mkdir -p protobuf ; travis_retry wget --no-check-certificate --quiet -O - ${PROTOBUF_URL} | tar --strip-components=1 -xz -C protobuf ; cd protobuf ; ./configure --prefix=/usr/local ; make ; else cd protobuf ; fi
+        make install
 
 # Change directory back to default build directory.
 before_script: