Minor shell cleanup; Travis CI build status icon (#194)

* Flip conditional for simplicity
* Indent lines
* Include Travis CI build status image & link

README.md

 # Scapy #
 
+[![Build Status](https://travis-ci.org/secdev/scapy.svg?branch=master)](https://travis-ci.org/secdev/scapy)
+
 Scapy is a powerful Python-based interactive packet manipulation
 program and library.
 

test/run_tests

@@ -5,7 +5,7 @@ if python --version 2>&1 | grep -q '^Python 2'; then
 else
     PYTHON=python2
 fi
-if [ ! -n "$*" ]
+if [ -z "$*" ]
 then
     PYTHONPATH=$DIR exec $PYTHON ${DIR}/scapy/tools/UTscapy.py -t regression.uts -f html -l -o /tmp/scapy_regression_test_$(date +%Y%m%d-%H%M%S).html
 else