ENH: Fix "build.sh" to allow exection from any directory

CMake/CircleCI/build.sh

@@ -1,6 +1,10 @@
-#!/bin/sh
+#!/bin/bash
 
 script_dir="`cd $(dirname $0); pwd`"
 
+pushd $script_dir
+
 docker build -t commontk/ctk-test:opengl-qt4 $script_dir -f Dockerfile-qt4
 docker build -t commontk/ctk-test:opengl-qt5 $script_dir -f Dockerfile-qt5
+
+popd