Proving script generates unexpected/wrong formatted(?) data

[ewynx]

When executing bash scripts/bench_proving_time.sh -m
A textfile for U256 is generated with this data:

[cols="<,>,>,>,>"]
|===
| Command 
| Mean [ms] 
| Min [ms] 
| Max [ms] 
| Relative 

| `bb prove -b ./target/bigint_benchmarking.json -w ./target/witness.gz -o ./target/proof` 
| 1100.1 ± 72.1 
| 1039.3 
| 1279.5 
| 1.00 
|===