Fix warnings

Author: ajalt

clikt/src/main/kotlin/com/github/ajalt/clikt/core/CliktCommand.kt

@@ -308,12 +308,12 @@ abstract class CliktCommand(
 
 /** Add the given commands as a subcommand of this command. */
 fun <T : CliktCommand> T.subcommands(commands: Iterable<CliktCommand>): T = apply {
-    _subcommands += commands
+    _subcommands = _subcommands + commands
 }
 
 /** Add the given commands as a subcommand of this command. */
 fun <T : CliktCommand> T.subcommands(vararg commands: CliktCommand): T = apply {
-    _subcommands += commands
+    _subcommands = _subcommands + commands
 }
 
 /**

clikt/src/main/kotlin/com/github/ajalt/clikt/output/text.kt

@@ -26,11 +26,11 @@ internal fun splitParagraphs(text: String): List<String> {
     while (i < text.length) {
         val end = if (text.startsWith("```", startIndex = i)) {
             PRE_P_END_REGEX.find(text, startIndex = i + 3)?.let {
-                (it.range.start + 3)..it.range.last
+                (it.range.first + 3)..it.range.last
             }
         } else {
             PLAIN_P_END_REGEX.find(text, startIndex = i)?.let {
-                if (it.value.endsWith("```")) it.range.start..(it.range.last - 3)
+                if (it.value.endsWith("```")) it.range.first..(it.range.last - 3)
                 else it.range
             }
         } ?: text.length..text.length

clikt/src/main/kotlin/com/github/ajalt/clikt/parameters/groups/ParameterGroup.kt

@@ -6,8 +6,6 @@ import com.github.ajalt.clikt.core.GroupableOption
 import com.github.ajalt.clikt.core.ParameterHolder
 import com.github.ajalt.clikt.output.HelpFormatter
 import com.github.ajalt.clikt.parameters.options.Option
-import com.github.ajalt.clikt.parameters.options.OptionDelegate
-import com.github.ajalt.clikt.parameters.options.longestName
 import com.github.ajalt.clikt.parsers.OptionParser
 import kotlin.properties.ReadOnlyProperty
 import kotlin.reflect.KProperty