Fixing typo.

src/QGCFileDialog.h

@@ -123,7 +123,7 @@ public:
         Options options = 0);
 
 private slots:
-    /// @brief The exec slot is private becasue we only want QGCFileDialog users to use the static methods. Otherwise it will break
+    /// @brief The exec slot is private because we only want QGCFileDialog users to use the static methods. Otherwise it will break
     ///        unit testing.
     int exec(void) { return QGCFileDialog::exec(); }