Linting fixes

[ModeSevenIndustrialSolutions]

An update to the linting setup has flagged the following code issues:

check builtin type constructor use.......................................Failed
- hook id: check-builtin-literals
- exit code: 1

src/hazard/onboard/wri_aqueduct_water_risk.py:108:49: replace dict() with {}
src/hazard/onboard/wri_aqueduct_water_risk.py:198:38: replace dict() with {}
src/hazard/onboard/wri_aqueduct_water_risk.py:479:47: replace dict() with {}
src/hazard/onboard/ethz_litpop.py:142:47: replace dict() with {}

Validate pyproject.toml..................................................Failed
- hook id: validate-pyproject
- exit code: 1

Invalid file: pyproject.toml
[ERROR] `data` must not contain {'meta`data`'} properties

In addition, some minor documentation updates are required:

README.md:60 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "```"]
README.md:76 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "```"]
src/hazard/onboard/flopros_flood.md:1 MD041/first-line-heading/first-line-h1 First line in a file should be a top-level heading [Context: "Global data set of protection ..."]
src/hazard/onboard/iris_wind.md:1 MD041/first-line-heading/first-line-h1 First line in a file should be a top-level heading [Context: "Sparks, N., Toumi, R. The Impe..."]
src/hazard/onboard/wisc_european_winter_storm.md:1 MD041/first-line-heading/first-line-h1 First line in a file should be a top-level heading [Context: "Maximum 10 metre 3 second gust..."]
src/hazard/onboard/wri_aqueduct_flood.md:1 MD041/first-line-heading/first-line-h1 First line in a file should be a top-level heading [Context: "The World Resources Institute ..."]

[xbarra]

We will handle them with #136
cc @violetacc