Fix the link to the 2.0 upgrade guide

[DavidBadura]

The navigation pointed to UPGRADE-2.0md, the dot before the extension was missing, so the "Upgrade from 1.x" entry led to a file that does not exist.

[github-actions]

Hello 👋

Here are the most recent benchmark results, compared against 2.1.x. Time is the mode over the iterations in the its column, with the relative standard deviation in brackets.

StackHydrator

subject	revs	its	memory	base	current	diff
benchHydrate1Object	1000	5	1.855mb -21.23%	1.260μs (±2.72%)	1.264μs (±2.82%)	+0.30%
benchExtract1Object	1000	5	1.855mb -21.23%	1.468μs (±1.09%)	1.430μs (±1.58%)	-2.56%
benchHydrate1000Objects	3	5	1.855mb -21.23%	1.225ms (±0.34%)	1.242ms (±1.59%)	+1.44%
benchExtract1000Objects	3	5	1.855mb 0.00%	1.202ms (±5.41%)	1.182ms (±1.73%)	-1.69%

StackHydratorWithLazy

subject	revs	its	memory	base	current	diff
benchHydrate1Object	1000	5	1.855mb 0.00%	0.195μs (±5.01%)	0.201μs (±6.86%)	+3.22%
benchHydrate1ObjectTriggerInit	1000	5	1.855mb 0.00%	1.617μs (±3.60%)	1.623μs (±1.19%)	+0.37%
benchHydrate1000Objects	3	5	1.855mb 0.00%	189.598μs (±2.72%)	189.108μs (±2.90%)	-0.26%
benchHydrate1000ObjectsTriggerInit	3	5	1.855mb 0.00%	1.596ms (±1.05%)	1.600ms (±0.56%)	+0.24%

StackHydratorWithCryptography

subject	revs	its	memory	base	current	diff
benchHydrate1Object	1000	5	1.855mb 0.00%	1.888μs (±1.50%)	1.850μs (±1.45%)	-2.02%
benchExtract1Object	1000	5	1.855mb 0.00%	4.952μs (±0.74%)	4.887μs (±0.63%)	-1.30%
benchHydrate1000Objects	3	5	1.855mb 0.00%	1.840ms (±0.80%)	1.856ms (±1.17%)	+0.91%
benchExtract1000Objects	3	5	1.855mb 0.00%	4.670ms (±0.88%)	4.690ms (±0.65%)	+0.43%

This comment gets updated every time a new commit comes in.