This 's oúr | uság' | alwéy, | &c.
So again, in the Knight's Tale, 233 (A 1091):—
We mót | endúr' | it thís 's | the shórt | and pleýn.
And again, in the same, 885 (A 1743):—
And seíd | e thís 's | a shórt | conclú | sioun.
And frequently elsewhere. In the present case, both this and is are unaccented, which is much harsher than when this bears an accent.
I find that Ten Brink has also noted this peculiarity, in his Chaucers Sprache, § 271. He observes that, in C. T. Group E, 56, the Ellesmere and Hengwrt MSS. actually substitute this for this is; see footnote; and hence note that the correct reading is—'But this his tale, which,' &c. See This in Schmidt, Shak. Lexicon. Cf. l. 620.
413. Com, came. The o is long; A.S. cóm, Goth. kwam.
417. 'I choose the formel to be my sovereign lady, not my mate.'
421. 'Beseeching her for mercy,' &c.