Fixed some Travis build errors

Author: Bas-Jan 't Jong

src/PhpWord/Style/Line.php

@@ -117,7 +117,7 @@ public function setFlip($value = null)
      *
      * @return boolean
      */
-    public function getFlip()
+    public function isFlip()
     {
         return $this->flip;
     }

src/PhpWord/Writer/Word2007/Style/Line.php

@@ -124,13 +124,17 @@ private function getElementStyle(LineStyle $style)
                 $styles[$key] = $value . 'px';
             }
         }
-        if ($style->getFlip()) {
+        if ($style->isFlip()) {
             $styles['flip']='y';
         }
 
         return $styles;
     }
 
+    /**
+     * Write Line stroke
+     *
+     */
     public function writeStroke()
     {
         $style = $this->getStyle();