Typos/misspellings

Closes microbit-foundation/python-editor-v3#1125
Closes microbit-foundation/python-editor-v3#1119
Closes #89

Author: microbit-matt-hillsdon

lang/en/typeshed/stdlib/math.pyi

@@ -159,7 +159,7 @@ def isinf(x: float) -> bool:
     ...
 
 def isnan(x: float) -> bool:
-    """Check is a value is not-a-number (NaN).
+    """Check if a value is not-a-number (NaN).
 
     Example: ``math.isnan(float('nan'))``
 

lang/en/typeshed/stdlib/microbit/__init__.pyi

@@ -132,7 +132,7 @@ def running_time() -> int:
     """
 
 def temperature() -> int:
-    """Get the temperature of the micro:bit in degrees Celcius."""
+    """Get the temperature of the micro:bit in degrees Celsius."""
 
 def set_volume(v: int) -> None:
     """Sets the volume.

lang/en/typeshed/stdlib/microbit/i2c.pyi

@@ -34,7 +34,7 @@ def scan() -> List[int]:
     ...
 
 def read(addr: int, n: int, repeat: bool = False) -> bytes:
-    """Read bytes from a device..
+    """Read bytes from a device.
 
     Example: ``i2c.read(0x50, 64)``