docs: fix @example macro

Author: alyst

doc/source/hclust.md

@@ -12,7 +12,8 @@ hclust
 Hclust
 ```
 
-```@example Single-linkage clustering using distance matrix
+Single-linkage clustering using distance matrix:
+```@example
 using Clustering
 D = rand(1000, 1000);
 D += D'; # symmetric distance matrix (optional)

doc/source/kmeans.md

@@ -27,7 +27,7 @@ kmeans!
 
 ## Examples
 
-```@example julia
+```@example
 using Clustering
 
 # make a random dataset with 1000 random 5-dimensional points
@@ -43,7 +43,8 @@ c = counts(R) # get the cluster sizes
 M = R.centers # get the cluster centers
 ```
 
-```@example Scatter plot of the K-means clustering results
+Scatter plot of the K-means clustering results:
+```@example
 using RDatasets, Clustering, Plots
 iris = dataset("datasets", "iris"); # load the data