Memory Leak

[JohnCMcDonough]

It appears that the keys in the context map that are set, but never removed. In context.js, _contexts keys are set using namespace._contexts.set(asyncId, namespace.active); and deleted using namespace._contexts.delete(currentUid); where currentUid is the executionAsyncId, not the id passed into the async hook handler.

A sample of one of the crashes observed due to this issue is given below.

<--- Last few GCs --->

[1:0x5595a7ffd9c0] 19367966 ms: Scavenge 1154.7 (1414.3) -> 1141.3 (1414.3) MB, 17.0 / 0.5 ms  allocation failure 
[1:0x5595a7ffd9c0] 19370410 ms: Scavenge 1155.5 (1414.3) -> 1143.5 (1414.3) MB, 40.5 / 0.8 ms  allocation failure 
[1:0x5595a7ffd9c0] 19375363 ms: Scavenge 1157.7 (1414.3) -> 1145.2 (1414.3) MB, 19.9 / 0.5 ms  allocation failure 
[1:0x5595a7ffd9c0] 19375870 ms: Scavenge 1159.7 (1414.3) -> 1147.3 (1414.3) MB, 43.5 / 0.7 ms  allocation failure 


<--- JS stacktrace --->

==== JS stack trace =========================================

Security context: 0x16617801bbd9 <JS Object>
    1: set [native collection.js:~247] [pc=0x661da70922b](this=0x4840a2843c1 <a Map with map 0x3dfb28a94319>,p=25597058,x=0x6c3ab1fb699 <an Object with map 0x7c2351f0fc1>)
    2: 0x1bf1c91c2ed9 <Symbol: init>(aka init) [/src/node_modules/cls-hooked/context.js:~290] [pc=0x661da7bfffd](this=0x1fd338a7e599 <an AsyncHook with map 0x3dfb28af8d91>,asyncId=25597058,type=0x166178074701 <String[7]: PROM...

FATAL ERROR: invalid table size Allocation failed - JavaScript heap out of memory

fix: #10