Use non breaking spaces.

As reported by zoffixznet <#1719>
it is better to use non-breaking spaces when dealing with Perl 5|6 to
ensure the version number does not wrapped onto a new line.

Fixed also a missing whitespace between two words.

Author: fluca1978

doc/Language/5to6-nutshell.pod6

@@ -899,9 +899,9 @@ The C<for> loop has the following rules:
 appearing after the list and an added arrow operator;
 =item the iteration variable is now always lexical: C<my> is neither needed nor
 allowed;
-=item the iteration variable is a I<read-only> alias to the current list element (in Perl 5
+=item the iteration variable is a I<read-only> alias to the current list element (in Perl 5
 it is a I<read-write> alias!). If a read-write alias is required, change the C«->»  before the iteration
-variable to a C«<->». When translatingfrom Perl 5, inspect the use of the loop variable to decide if
+variable to a C«<->». When translating from Perl 5, inspect the use of the loop variable to decide if
 read-write is needed.
 
 =for code :lang<perl5>