fix grammar typo

removed repeated 'for'

Author: medavox

docs/coroutines-guide.md

@@ -2,7 +2,7 @@
 Kotlin, as a language, provides only minimal low-level APIs in its standard library to enable various other 
 libraries to utilize coroutines. Unlike many other languages with similar capabilities, `async` and `await`
 are not keywords in Kotlin and are not even part of its standard library. Moreover, Kotlin's concept
-of _suspending function_ provides a safer and less error-prone abstraction for for asynchronous 
+of _suspending function_ provides a safer and less error-prone abstraction for asynchronous 
 operations than futures and promises.  
 
 `kotlinx.coroutines` is a rich library for coroutines developed by JetBrains. It contains a number of high-level 
@@ -29,4 +29,4 @@ In order to use coroutines as well as follow the examples in this guide, you nee
 * [Guide to UI programming with coroutines](../ui/coroutines-guide-ui.md)
 * [Guide to reactive streams with coroutines](../reactive/coroutines-guide-reactive.md)
 * [Coroutines design document (KEEP)](https://github.com/Kotlin/kotlin-coroutines/blob/master/kotlin-coroutines-informal.md)
-* [Full kotlinx.coroutines API reference](http://kotlin.github.io/kotlinx.coroutines)
+* [Full kotlinx.coroutines API reference](http://kotlin.github.io/kotlinx.coroutines)