try to fix stupid travis build failing

because of stupid pandoc version html is not exactly the same with
double space when converting MD.

tests/ipynbref/IntroNumPy.orig.html

@@ -2822,8 +2822,7 b' The sum of elements along the columns is : [ 4 6 8 10]'
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-<p>As you can see in this example, the value of the <code>axis</code> parameter is the dimension which will be <em>consumed</em> once the operation has been carried out.  This is why to sum along the rows we use <code>axis=0</code>.<br />
-</p>
+<p>As you can see in this example, the value of the <code>axis</code> parameter is the dimension which will be <em>consumed</em> once the operation has been carried out.  This is why to sum along the rows we use <code>axis=0</code>.</p>
 <p>This can be easily illustrated with an example that has more dimensions; we create an array with 4 dimensions and shape <code>(3,4,5,6)</code> and sum along the axis number 2 (i.e. the <em>third</em> axis, since in Python all counts are 0-based).  That consumes the dimension whose length was 5, leaving us with a new array that has shape <code>(3,4,6)</code>:</p>
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