Use consistent implementation for Node::peephole()

[fuhsnn]

The logic is same but only ch4 has this version.

Simple/chapter03/src/main/java/com/seaofnodes/simple/node/Node.java

Line 236 in dd907c2

if( obs != null ) obs.after(this, n == null && old == _type ? null : rez, false);

Simple/chapter04/src/main/java/com/seaofnodes/simple/node/Node.java

Line 239 in dd907c2

if( obs != null ) obs.after(this, n != null || old != _type ? rez : null, false);

Simple/chapter05/src/main/java/com/seaofnodes/simple/node/Node.java

Line 240 in dd907c2

if( obs != null ) obs.after(this, n == null && old == _type ? null : rez, false);

[cliffclick]

LGTM