Update LFWRBMExample.java

fixed a typo in a comment, which would have appeared in a gist
Update RawDBNMnistExample.java
Fix potential null pointer exception in yield()

Using the method children() initializes the property children if it is null.
Using the property directly results in a null pointer exception in that case.
Merge pull request #59 from danielhers/patch-1

Fix potential null pointer exception in yield()