Bump klib ABI version

KLIB forward compatibility was broken during work related to
definitely not-null types, but version was not changed. This led to
exceptions in compiler instead of meaningful error.

^KT-52518

compiler/util-klib/src/org/jetbrains/kotlin/library/KotlinAbiVersion.kt

@@ -60,6 +60,6 @@ data class KotlinAbiVersion(val major: Int, val minor: Int, val patch: Int) {
     override fun toString() = "$major.$minor.$patch"
 
     companion object {
-        val CURRENT = KotlinAbiVersion(1, 6, 0)
+        val CURRENT = KotlinAbiVersion(1, 7, 0)
     }
 }