Update gnuplot requirement from 0.0.42 to 0.0.43

---
updated-dependencies:
- dependency-name: gnuplot
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

examples/observer/Cargo.toml

@@ -9,5 +9,5 @@ publish = false
 argmin = { version = "*", path = "../../crates/argmin" }
 argmin-math = { version = "*", features = ["vec"], path = "../../crates/argmin-math" }
 argmin_testfunctions = { version = "*", path = "../../crates/argmin-testfunctions" }
-gnuplot = "0.0.42"
+gnuplot = "0.0.43"
 instant = "0.1.12"