BLD: always install the latest tf in configure.sh (#587)

Author: facaiy

configure.sh

@@ -39,9 +39,9 @@ function generate_shared_lib_name() {
   fi
 }
 
-QUIET_FLAG=""
+PIP_INSTALL_OPTS="--upgrade"
 if [[ $1 == "--quiet" ]]; then
-    QUIET_FLAG="--quiet"
+    PIP_INSTALL_OPTS="$PIP_INSTALL_OPTS --quiet"
 elif [[ ! -z "$1" ]]; then
     echo "Found unsupported args: $@"
     exit 1
@@ -57,7 +57,7 @@ esac
 BUILD_DEPS_DIR=build_deps
 REQUIREMENTS_TXT=$BUILD_DEPS_DIR/requirements.txt
 
-${PYTHON_VERSION:=python} -m pip install $QUIET_FLAG -r $REQUIREMENTS_TXT
+${PYTHON_VERSION:=python} -m pip install $PIP_INSTALL_OPTS -r $REQUIREMENTS_TXT
 
 [[ -f .bazelrc ]] && rm .bazelrc