travis: added m4 dir for libstrophe

.travis.yml

@@ -4,6 +4,7 @@ install:
     - sudo apt-get -y install libssl-dev libexpat1-dev libncursesw5-dev libglib2.0-dev libnotify-dev libcurl3-dev libxss-dev libotr2-dev
     - git clone git://github.com/strophe/libstrophe.git
     - cd libstrophe
+    - mkdir m4
     - ./bootstrap.sh
     - ./configure --prefix=/usr
     - make