bump(rust): bumps Rust to 1.50

[baszalmstra]

Bumps rust to 1.50.

[codecov]

Codecov Report

Merging #310 (e8c395c) into master (df03295) will increase coverage by 0.00%.
The diff coverage is 54.00%.

@@           Coverage Diff           @@
##           master     #310   +/-   ##
=======================================
  Coverage   80.89%   80.90%           
=======================================
  Files         242      242           
  Lines       14716    14689   -27     
=======================================
- Hits        11905    11884   -21     
+ Misses       2811     2805    -6     

Impacted Files	Coverage Δ
crates/mun_hir/src/ty/infer.rs	69.28% <ø> (ø)
crates/mun_language_server/src/state.rs	88.35% <ø> (ø)
crates/mun_language_server/src/state/protocol.rs	36.84% <0.00%> (ø)
crates/mun_memory/src/diff/myers.rs	100.00% <ø> (ø)
crates/mun_hir/src/package_defs/collector.rs	82.32% <77.27%> (-0.03%)	⬇️
crates/mun_codegen/src/code_gen/symbols.rs	94.81% <100.00%> (ø)
crates/mun_codegen/src/ir/body.rs	79.79% <100.00%> (ø)
crates/mun_codegen/src/ir/type_table.rs	91.91% <100.00%> (ø)
crates/mun_codegen/src/value/array_value.rs	77.77% <100.00%> (ø)
...ates/mun_syntax/src/parsing/grammar/expressions.rs	96.28% <100.00%> (+0.75%)	⬆️
... and 1 more

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