Changing "mkdir build -p" to "mkdir -p build"

Putting the command-line switch first on the line for OSX
compatibility. Linux handles it ok either way.

build.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 
-mkdir build -p
+mkdir -p build
 cd build
 qmake ../xastir-qt.pro
 make