fix a typo

Author: daisukebe

docs/programming-guide.md

@@ -48,7 +48,7 @@ import org.apache.spark.SparkContext
 import org.apache.spark.SparkConf
 {% endhighlight %}
 
-(Before Spark 1.3.0, you need to explicitly import `import org.apache.spark.SparkContext._` to enable essential implicit conversions.)
+(Before Spark 1.3.0, you need to explicitly `import org.apache.spark.SparkContext._` to enable essential implicit conversions.)
 
 </div>