Contributing: fix typos (#3125)

meetings/2015/LDM-2015-01-28.md

@@ -274,7 +274,7 @@ A value-semantics class like the above would be automatically generated by a "re
 class Point(int X, int Y);
 ```
 
-By default, this would generate all of the above, except parameter names would be upper case. If you want to supercede default behavior, you can give it a body and do that explicitly. For instance, you could make X mutable:
+By default, this would generate all of the above, except parameter names would be upper case. If you want to supersede default behavior, you can give it a body and do that explicitly. For instance, you could make X mutable:
 
 ``` c#
 class Point(int X, int Y)

meetings/2019/LDM-2019-04-29.md

@@ -13,7 +13,7 @@
 
 The way `base.` works in classes, if the base implementation that was present at compile
 time is removed at rune time, the CLR will search for the next implementation in the
-heirarchy and use that instead. For example,
+hierarchy and use that instead. For example,
 
 ```C#
 class A

meetings/2019/LDM-2019-08-26.md

@@ -25,7 +25,7 @@ This is the next major release (as C# 8.0 is a done deal at this point). Putting
 
 ## #146
 
-There's something to this, but instead of marking seperately, we think it is paired with allowing nullary constructors on structs . For those we would warn on uses of `default(S)` that we can detect, similar to nullability.
+There's something to this, but instead of marking separately, we think it is paired with allowing nullary constructors on structs . For those we would warn on uses of `default(S)` that we can detect, similar to nullability.
 
 ## #812
 

proposals/csharp-8.0/async-streams.md

@@ -168,7 +168,7 @@ Consider `IAsyncEnumerable<int> GetData([EnumeratorCancellation] CancellationTok
 The implementer of this method can simply use the parameter in the method body. 
 The consumer can use either consumption patterns above:
 1. if you use `GetData(token)`, then the token is saved into the async-enumerable and will be used in iteration,
-2. if you use `givenIAsyncEnumerable.WithCancellation(token)`, then the token passed to `GetAsyncEnumerator` will supercede any token saved in the async-enumerable.
+2. if you use `givenIAsyncEnumerable.WithCancellation(token)`, then the token passed to `GetAsyncEnumerator` will supersede any token saved in the async-enumerable.
 
 ## foreach