Fix a typo of "threshold"

mengxr

Author: Xusen Yin <yinxusen@gmail.com>

Closes #5769 from yinxusen/patch-1 and squashes the following commits:

43235f4 [Xusen Yin] Update PearsonCorrelation.scala
f7287ee [Xusen Yin] Fix a typo of "threshold"

mllib/src/main/scala/org/apache/spark/mllib/stat/correlation/PearsonCorrelation.scala

@@ -101,7 +101,7 @@ private[stat] object PearsonCorrelation extends Correlation with Logging {
     Matrices.fromBreeze(cov)
   }
 
-  private def closeToZero(value: Double, threshhold: Double = 1e-12): Boolean = {
-    math.abs(value) <= threshhold
+  private def closeToZero(value: Double, threshold: Double = 1e-12): Boolean = {
+    math.abs(value) <= threshold
   }
 }