Fixes knife_edge() output

knife_edge.py

@@ -63,4 +63,4 @@ def knife_edge(nrun, axisKey='scannerX', signalKey='FastADC4peaks', p0=None, plo
         plt.ylabel(signalKey)
         plt.xlabel(axisKey + '-position [mm]')
         plt.tight_layout()
-    return np.array(popt[1], pcov[1,1]**0.5)
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+    return np.array([popt[1], pcov[1,1]**0.5])
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