Fix typos and terminology issues (#339)

Author: Chris Cho

source/fundamentals/builders/aggregates.txt

@@ -639,7 +639,7 @@ ReplaceRoot
 Use the ``replaceRoot()`` method to create a :manual:`$replaceRoot </reference/operator/aggregation/replaceRoot/>`
 pipeline stage that replaces each input document with the specified document.
 
-The following example replaces each input document with the subdocument
+The following example replaces each input document with the nested document
 in the ``spanish_translation`` field:
 
 .. literalinclude:: /includes/fundamentals/code-snippets/builders/AggBuilders.java

source/fundamentals/builders/projections.txt

@@ -300,7 +300,7 @@ The following code shows the output from this projection:
      "year": 2018,
      "type": "even number but not a leap year",
      "temperatures": [
-         ... <January-June temperature subdocuments>
+         ... <January-June temperature nested documents>
      ]
    }
    {
@@ -310,7 +310,7 @@ The following code shows the output from this projection:
      "year": 2019,
      "type": "odd number, can't be a leap year",
      "temperatures": [
-         ... <January-June temperature subdocuments>
+         ... <January-June temperature nested documents>
      ]
    }
 
@@ -334,7 +334,7 @@ The following code shows the output from this projection:
      "year": 2018,
      "type": "even number but not a leap year",
      "temperatures": [
-         ... <July-December temperature subdocuments>
+         ... <July-December temperature nested documents>
      ]
    }
    {
@@ -344,7 +344,7 @@ The following code shows the output from this projection:
      "year": 2019,
      "type": "odd number, can't be a leap year",
      "temperatures": [
-         ... <July-December temperature subdocuments>
+         ... <July-December temperature nested documents>
      ]
    }
 

source/fundamentals/databases-collections.txt

@@ -145,7 +145,7 @@ Specify Read Preferences, Read Concerns, and  Write Concerns
 ------------------------------------------------------------
 
 **Read preferences**, **read concerns**, and **write concerns** control
-how the driver routes read operations and waits for acknowledgement for
+how the driver routes read operations and waits for acknowledgment for
 read and write operations when connected to a MongoDB replica set.
 Read preferences and read concerns apply to all read operations;
 write concerns apply to all write operations.