fix: singularize 'analyses' to 'analysis' instead of 'analyasis'

[greymoth-jp]

singularize('analyses') returns analyasis, which isn't a word. It should return analysis.

pluralize('analysis') already gives analyses, so singularize is just failing to invert it.

The cause is the replacement string on the -ses -> -sis rule:

[regex.plural.analyses, '$1$2sis'],

The regex is ((a)naly|(b)a|(d)iagno|(p)arenthe|(p)rogno|(s)ynop|(t)he)ses$. $1 is the full stem (analy, ba, diagno, ...), and the inner letter groups are $2 for (a), $3 for (b), $4 for (d), and so on. The template uses $2, but $2 is only ever set on the (a)naly branch, so it re-appends a stray a: analy + a + sis = analyasis. For every other word $2 is empty, which is why bases, diagnoses, parentheses, prognoses, synopses, theses already singularize correctly.

$1 already contains that a, so dropping $2 fixes analyses and leaves the other six untouched:

[regex.plural.analyses, '$1sis'],

Added assertions for analyses, bases and diagnoses in the singularize test to lock the family. Full suite passes.