Bump simpleclient_httpserver from 0.14.1 to 0.15.0

Bumps [simpleclient_httpserver](https://github.com/prometheus/client_java) from 0.14.1 to 0.15.0.
- [Release notes](https://github.com/prometheus/client_java/releases)
- [Commits](https://github.com/prometheus/client_java/compare/parent-0.14.1...parent-0.15.0)

---
updated-dependencies:
- dependency-name: io.prometheus:simpleclient_httpserver
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

uhabits-server/build.gradle.kts

@@ -44,7 +44,7 @@ dependencies {
     implementation("io.ktor:ktor-jackson:$ktorVersion")
     implementation("org.jetbrains:kotlin-css-jvm:1.0.0-pre.148-kotlin-1.4.30")
     implementation("io.prometheus:simpleclient:0.14.1")
-    implementation("io.prometheus:simpleclient_httpserver:0.14.1")
+    implementation("io.prometheus:simpleclient_httpserver:0.15.0")
     implementation("io.prometheus:simpleclient_hotspot:0.15.0")
     testImplementation("io.ktor:ktor-server-tests:$ktorVersion")
     testImplementation("com.nhaarman.mockitokotlin2:mockito-kotlin:2.2.0")