Address some Kotlin language warnings

app/src/main/java/eu/kanade/tachiyomi/source/LocalSource.kt

@@ -84,9 +84,9 @@ class LocalSource(private val context: Context) : CatalogueSource {
         when (state?.index) {
             0 -> {
                 mangaDirs = if (state.ascending) {
-                    mangaDirs.sortedBy { it.name.toLowerCase(Locale.ENGLISH) }
+                    mangaDirs.sortedBy { it.name.lowercase(Locale.ENGLISH) }
                 } else {
-                    mangaDirs.sortedByDescending { it.name.toLowerCase(Locale.ENGLISH) }
+                    mangaDirs.sortedByDescending { it.name.lowercase(Locale.ENGLISH) }
                 }
             }
             1 -> {
@@ -238,7 +238,7 @@ class LocalSource(private val context: Context) : CatalogueSource {
     }
 
     private fun isSupportedFile(extension: String): Boolean {
-        return extension.toLowerCase(Locale.ROOT) in SUPPORTED_ARCHIVE_TYPES
+        return extension.lowercase() in SUPPORTED_ARCHIVE_TYPES
     }
 
     fun getFormat(chapter: SChapter): Format {

app/src/main/java/eu/kanade/tachiyomi/source/online/HttpSource.kt

@@ -54,7 +54,7 @@ abstract class HttpSource : CatalogueSource {
      * Note the generated id sets the sign bit to 0.
      */
     override val id by lazy {
-        val key = "${name.toLowerCase()}/$lang/$versionId"
+        val key = "${name.lowercase()}/$lang/$versionId"
         val bytes = MessageDigest.getInstance("MD5").digest(key.toByteArray())
         (0..7).map { bytes[it].toLong() and 0xff shl 8 * (7 - it) }.reduce(Long::or) and Long.MAX_VALUE
     }
@@ -80,7 +80,7 @@ abstract class HttpSource : CatalogueSource {
     /**
      * Visible name of the source.
      */
-    override fun toString() = "$name (${lang.toUpperCase()})"
+    override fun toString() = "$name (${lang.uppercase()})"
 
     /**
      * Returns an observable containing a page with a list of manga. Normally it's not needed to